[infra] remove custom import path from Travis

Travis was hard-coded to a custom import path due to capitalization in
the previous repo location's import path.  This is no longer needed, and
the hard-coding breaks when in the current location.

.travis.yml

@@ -3,9 +3,6 @@ language: go
 go:
 - 1.8
 
-# blech, Travis downloads with capitals in DirectXMan12, which confuses go
-go_import_path: github.com/directxman12/custom-metrics-boilerplate
-
 addons:
   apt:
     sources: