fix for heroku ci (#392)

* attempted fix

* added a comment

* fixes

* improved changelog

CHANGELOG.md

 # Python Buildpack Changelog
 
+## 103
+
+Bug fixes and improvements.
+
+- Fix for Pipenv.
+- Fix for Heroku CI.
+- Improve handling of WEB_CONCURRENCY when using multiple buildpacks.
+- Adjust environment variables set during the build to more closely match those in the dyno environment (DYNO is now available, STACK is not).
+- Restore the build cache prior to running bin/pre_compile.
+
 ## 102
 
 Buildpack code cleanup.

bin/compile

@@ -192,8 +192,12 @@ sub-env $BIN_DIR/steps/nltk
 mtime "nltk.download.time" "${start}"
 
 # Support for pip install -e.
-rm -fr $BUILD_DIR/.heroku/src
-deep-cp /app/.heroku/src $BUILD_DIR/.heroku/src
+# In CI, $BUILD_DIR is /app.
+if [[ ! "$BUILD_DIR" == "/app" ]]; then
+  rm -fr $BUILD_DIR/.heroku/src
+  deep-cp /app/.heroku/src $BUILD_DIR/.heroku/src
+fi
+
 
 # Django collectstatic support.
 let start=$(nowms)