Allow environment variables during pip install, fixes #416 (#417)

* Allow environment variables during pip install, fixes #416

* shift sub-env command, fix typo

* bash check thingy fixed

bin/steps/pip-install

@@ -6,7 +6,7 @@ if [ ! "$SKIP_PIP_INSTALL" ]; then
     puts-step "Installing requirements with pip"
 
     set +e
-    /app/.heroku/python/bin/pip install -r "$BUILD_DIR/requirements.txt" --exists-action=w --src=/app/.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | tee "$WARNINGS_LOG" | cleanup | indent
+    sub-env /app/.heroku/python/bin/pip install -r "$BUILD_DIR/requirements.txt" --exists-action=w --src=/app/.heroku/src --disable-pip-version-check --no-cache-dir 2>&1 | tee "$WARNINGS_LOG" | cleanup | indent
     PIP_STATUS="${PIPESTATUS[0]}"
     set -e
 
@@ -22,4 +22,4 @@ if [ ! "$SKIP_PIP_INSTALL" ]; then
     /app/.heroku/python/bin/pip freeze --disable-pip-version-check > .heroku/python/requirements-installed.txt
 
     echo
-fi
+fi

bin/steps/pipenv

@@ -18,4 +18,4 @@ if [[ -f Pipfile ]]; then
         /app/.heroku/python/bin/pip freeze > requirements.txt
 
     fi
-fi
+fi

bin/utils

@@ -72,7 +72,7 @@ sub-env() {
       done
     fi
 
-    $1
+    "$@"
 
   )
 }