Upgrade to pip 19.2.3

Bump PIP_UPDATE from 9.0.2 to 19.2.3. This variable is used in bin/steps/python
to determine which pip version to install or upgrade to.

Author: cjolowicz

bin/compile

@@ -59,7 +59,7 @@ PY27="python-2.7"
 # Which stack is used (for binary downloading), if none is provided (e.g. outside of Heroku)?
 DEFAULT_PYTHON_STACK="cedar-14"
 # If pip doesn't match this version (the version we install), run the installer.
-PIP_UPDATE="9.0.2"
+PIP_UPDATE="19.2.3"
 
 export DEFAULT_PYTHON_STACK PIP_UPDATE
 export PY37 PY36 PY35 PY27 PY34