Run our .travis.yml through the lint check (#5599)

.travis.yml

@@ -5,29 +5,23 @@ matrix:
   include:
   - php: 7.0
   - php: 5.3
-    env:
-      SKIP_STYLE_CHECK=1
+    env: SKIP_STYLE_CHECK=1
   - php: 5.4
-    env:
-      SKIP_STYLE_CHECK=1
+    env: SKIP_STYLE_CHECK=1
   - php: 5.5
-    env:
-      SKIP_STYLE_CHECK=1
+    env: SKIP_STYLE_CHECK=1
   - php: 5.6
-    env:
-      SKIP_STYLE_CHECK=1
-      EXECUTE_BUILD_DOCS=true
-  - php: hhvm
-    env:
-      SKIP_STYLE_CHECK=1
+    env: SKIP_STYLE_CHECK=1 EXECUTE_BUILD_DOCS=true
+#  - php: hhvm
+#    env: SKIP_STYLE_CHECK=1
 
   allow_failures:
   - php: hhvm
 
 cache:
-  - pip
-  - directories:
+  directories:
     - vendor
+    - $HOME/.cache/pip
     - $HOME/.composer/cache
 
 before_install: