Travis: Use virtual display server for electron-mocha

Author: lgeiger

.travis.yml

@@ -6,6 +6,7 @@ addons:
     sources:
     - ubuntu-toolchain-r-test
     packages:
+    - xvfb
     - gcc-4.9
     - g++-4.9
     - uuid-dev
@@ -25,6 +26,8 @@ env:
     secure: 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
 
 before_install:
+  - export DISPLAY=':99.0'
+  - Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &
   - curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.30.2/install.sh | bash
   - source ~/.nvm/nvm.sh
   - nvm install $NODE_VERSION