Fix package not found issue and provide error message

[IanDuncanT]

Package not found returns "Package not found. Try again." message and exits.
Resolve #15 and resolve #13

[Wabri]

Travis continue to throw errors, now for 2 reason:

1. Unable to download 3.7 archive. The archive may not exist.
2. No command 'inv' found
   The first point can be solve with this: https://github.com/mediascopegroup/light_rest_client/issues/2 .
   The second one I dont know what command is inv.

[IanDuncanT]

I found the inv from a different repository using Travis and I am trying to figure it out. The documentation isn’t that good for python on how to include command line arguments or type values once it starts

[Wabri]

There is a problem with python version 3.7, but in the other versions it works perfectly

[IanDuncanT]

@Wabri It works now! I am trying to figure out how to set a matrix of multiple environment variables to test it with all packages, for now it tests yapi.py on the file test.sh

[IanDuncanT]

Python 3.7 must use xenial and lower must use trusty for the dist