Add debugging information to Dockerfile
@@ -41,6 +41,9 @@ RUN gofmt -w .
# therefore reports that the file may have changed (ie, a series of 0s)
# See https://github.com/stripe/veneur/pull/110#discussion_r92843581
RUN git add .
+# The output will be empty unless the build fails, in which case this
+# information is helpful in debugging
+RUN git diff --cached
RUN git diff-index --cached --exit-code HEAD
