README.rst: Fix Link to Travis CI for macOS Build
README.rst: Fix Link to Travis CI for macOS Build

The shield for the macOS Build (Travis CI) now
points to https://travis-ci/coala/coala instead
of travis-ci.org/coala/coala.

Fixes https://github.com/coala/coala/issues/4273

kartikeys98/coala,karansingh1559/coala,coala/coala,arjunsinghy96/coala,coala/coala,karansingh1559/coala,Balaji2198/coala,rimacone/testing2,CruiseDevice/coala,damngamerz/coala,RJ722/coala,Asnelchristian/coala,damngamerz/coala,damngamerz/coala,Asnelchristian/coala,MariosPanag/coala,coala-analyzer/coala,aptrishu/coala,kartikeys98/coala,shreyans800755/coala,SanketDG/coala,jayvdb/coala,kartikeys98/coala,rimacone/testing2,Balaji2198/coala,RJ722/coala,coala-analyzer/coala,karansingh1559/coala,Nosferatul/coala,nemaniarjun/coala,Asalle/coala,coala-analyzer/coala,SanketDG/coala,rimacone/testing2,MariosPanag/coala,nemaniarjun/coala,coala/coala,CruiseDevice/coala,Asalle/coala,SanketDG/coala,arjunsinghy96/coala,shreyans800755/coala,Asalle/coala,shreyans800755/coala,aptrishu/coala,arjunsinghy96/coala,Balaji2198/coala,jayvdb/coala,jayvdb/coala,Asnelchristian/coala,aptrishu/coala,MariosPanag/coala,Nosferatul/coala,nemaniarjun/coala,RJ722/coala,CruiseDevice/coala,Nosferatul/coala