No início estava recebendo um erro de objeto não mapeado, 'org.hibernate....: Produto is not mapped' então peguei algumas classes de configuração (que eu achei que fossem o problema) do projeto final disponibilizado, daí o erro no log do Heroku mudou:
C:\Users\Matheus\Documents\workspace\casadocodigo>heroku logs
2019-01-03T18:44:53.356659+00:00 app[web.1]: at java.lang.reflect.Method.invoke(Method.java:498)
2019-01-03T18:44:53.356832+00:00 app[web.1]: at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
2019-01-03T18:44:53.357011+00:00 app[web.1]: at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133)
2019-01-03T18:44:53.357189+00:00 app[web.1]: at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97)
2019-01-03T18:44:53.357369+00:00 app[web.1]: at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
2019-01-03T18:44:53.357548+00:00 app[web.1]: at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
2019-01-03T18:44:53.357825+00:00 app[web.1]: at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
2019-01-03T18:44:53.357895+00:00 app[web.1]: at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
2019-01-03T18:44:53.358187+00:00 app[web.1]: at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
2019-01-03T18:44:53.358261+00:00 app[web.1]: at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
2019-01-03T18:44:53.358542+00:00 app[web.1]: at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
2019-01-03T18:44:53.358617+00:00 app[web.1]: at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
2019-01-03T18:44:53.358910+00:00 app[web.1]: at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
2019-01-03T18:44:53.358988+00:00 app[web.1]: at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
2019-01-03T18:44:53.362751+00:00 app[web.1]: at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
2019-01-03T18:44:53.362840+00:00 app[web.1]: at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
2019-01-03T18:44:53.362914+00:00 app[web.1]: at org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter.doFilterInternal(OpenEntityManagerInViewFilter.java:178)
2019-01-03T18:44:53.362986+00:00 app[web.1]: at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
2019-01-03T18:44:53.363057+00:00 app[web.1]: at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
2019-01-03T18:44:53.363133+00:00 app[web.1]: at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
2019-01-03T18:44:53.363197+00:00 app[web.1]: at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
2019-01-03T18:44:53.363259+00:00 app[web.1]: at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
2019-01-03T18:44:53.363313+00:00 app[web.1]: at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
2019-01-03T18:44:53.363370+00:00 app[web.1]: at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
2019-01-03T18:44:53.363427+00:00 app[web.1]: at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:317)
2019-01-03T18:44:53.363486+00:00 app[web.1]: at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:127)
2019-01-03T18:44:53.363543+00:00 app[web.1]: at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:91)
2019-01-03T18:44:53.363599+00:00 app[web.1]: at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:331)
2019-01-03T18:44:53.363657+00:00 app[web.1]: at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(E