Travis-ci: Do not download unecessary data from Github and only build the master branch.

.travis.yml

@@ -13,6 +13,13 @@ addons:
       - lmodern
       - latex2html
 
+branches:
+  only:
+  - master
+
+git:
+  depth: false
+
 script:
   - autoreconf -si
   - ./configure