Adding travis-cargo to build for docs

.travis.yml

@@ -1 +1,23 @@
 language: rust
+rust:
+  -stable
+
+# load travis-cargo
+before_script:
+  - |
+      pip install 'travis-cargo<0.2' --user &&
+      export PATH=$HOME/.local/bin:$PATH
+
+# the main build
+script:
+  - |
+      travis-cargo build &&
+      travis-cargo test &&
+      travis-cargo --only stable doc
+
+after_success:
+  - travis-cargo --only stable doc-upload
+
+env:
+  global:
+    secure: E/K+u8fhwLNKDvjG6kiuDumrXY/RMZOMa7SS88qhsPKStdHjNmaCwUFUe76RJDzMCqeN31u2mUwvMfMK3xDShABQjoD/tze/KbV5v6VTeL4vplHwZh6TzwaYKKBtNxL1q47A8FSTNK9PUbT+gEIAEY9Nadho7wKrYfT+CQxcb2A=