Merge pull request matplotlib#4170 from jenshnielsen/travis_docs_first_commit

Travis: Commit docs on top of first_commit

Author: tacaswell

.travis.yml

@@ -89,6 +89,7 @@ after_success:
     git clone [email protected]:matplotlib/devdocs.git
     cd devdocs
     git checkout --orphan gh-pages
+    git reset --hard first_commit
     cp -R ../matplotlib/doc/build/html/. .
     touch .nojekyll
     git config --global user.email "MatplotlibTravisBot@nomail"