.travis.yml: Update Golang version to 1.11.5
.travis.yml: Update Golang version to 1.11.5

Remove old golang repository links from .travis.yml

Setup gimme to install the latest stable version of golang
v1.11.5 available at the time of the change

Closes https://github.com/coala/coala-bears/issues/2843

coala-analyzer/coala-bears,coala/coala-bears,coala-analyzer/coala-bears,coala/coala-bears,coala/coala-bears,coala/coala-bears,coala/coala-bears,coala/coala-bears,coala-analyzer/coala-bears,coala/coala-bears,coala-analyzer/coala-bears,coala/coala-bears,coala/coala-bears,coala-analyzer/coala-bears,coala/coala-bears,coala-analyzer/coala-bears,coala-analyzer/coala-bears,coala-analyzer/coala-bears,coala-analyzer/coala-bears,coala/coala-bears,coala/coala-bears