Fix shields.io image URLs
Fix shields.io image URLs

Travis and Codecov shields in README.md should point to master branch,
and not scare users about (intentionally) failing ITs is side
branches...

rvais/xmvn,fedora-java/xmvn,mizdebsk/xmvn,rvais/xmvn,mizdebsk/xmvn,mizdebsk/xmvn,fedora-java/xmvn,rvais/xmvn,rvais/xmvn,mizdebsk/xmvn,fedora-java/xmvn