Adding missing packages to travis cache, removing duplicate yarn install directive

.travis.yml

@@ -6,6 +6,8 @@ cache:
   yarn: true
   directories:
     - node_modules
+    - packages/neutrino/node_modules
+    - packages/neutrino-middleware-banner/node_modules
     - packages/neutrino-middleware-chunk/node_modules
     - packages/neutrino-middleware-clean/node_modules
     - packages/neutrino-middleware-compile-loader/node_modules
@@ -31,7 +33,6 @@ cache:
     - packages/neutrino-preset-react/node_modules
     - packages/neutrino-preset-web/node_modules
 before_script:
-  - yarn
   - yarn bootstrap
 script:
   - yarn test