Amend UTF-8 encoding comment

Author: Donatien Garnier

.travis.yml

@@ -109,7 +109,7 @@ matrix:
     - <<: *basic-vm
       name: "UTF-8 Check"
       script:
-        # Make sure we're not introducing any non-UTF-8 character in text files
+        # Make sure we're not introducing any text which is not UTF-8 encoded
         - git diff $TRAVIS_BRANCH...HEAD -U0 | ( grep -a '^+' || true ) | ( ! grep -axv '.*' )
 
     - <<: *basic-vm