Change pip to pip3

Python 2.7 has reached end of support.

Author: devlinbd2

sample-apps/blank-python/2-build-layer.sh

@@ -2,4 +2,4 @@
 set -eo pipefail
 rm -rf package
 cd function
-pip install --target ../package/python -r requirements.txt
+pip3 install --target ../package/python -r requirements.txt