Fix indentation in .travis.yml

Author: phansch

.travis.yml

@@ -1,14 +1,14 @@
 language: rust
 matrix:
- include:
-   - rust: nightly
-     env: FEATURES=""
-   - rust: beta
-     env: FEATURES="--features stable"
-   - rust: stable
-     env: FEATURES="--features stable"
-   - rust: nightly
-     env: FEATURES="--features stable"
+  include:
+    - rust: nightly
+      env: FEATURES=""
+    - rust: beta
+      env: FEATURES="--features stable"
+    - rust: stable
+      env: FEATURES="--features stable"
+    - rust: nightly
+      env: FEATURES="--features stable"
 
 script: cd test-project && cargo test $FEATURES