Update .travis.yml

add platformio compilation test

.travis.yml

@@ -1,9 +1,18 @@
 sudo: false
 
-language: bash
+language: python
+ python:
+     - "2.7"
 
 os:
   - linux
+  
+cache:
+     directories:
+         - "~/.platformio"
+install:
+     - pip install -U platformio
+     - platformio update
 
 before_script:
   - wget http://downloads.arduino.cc/arduino-1.8.5-linux64.tar.xz
@@ -31,6 +40,7 @@ before_script:
   - mv $TRAVIS_BUILD_DIR/libraries/ESP32NETBIOS $HOME/arduino_ide/libraries/
     
 script:
+  - platformio run
   - cd $TRAVIS_BUILD_DIR
   - source command.sh
   - export PATH="$HOME/arduino_ide:$PATH"