Force Environment Variables to be Strings

[pickypg]

This forces any environment variables to be sent to GCF as strings, even if the value was supplied as a non-string (e.g., number).

This is necessary because GCF throws an error if it receives non-string values.

Fixes #128

[bao1018]

@pickypg I think it is a good idea, can you rebase and fix the conflicts then I can move forward ? thanks

[pickypg]

@bao1018 I've rebased and fixed the conflicts.