Use CI cloned version instead of master for @PlatformIO (#157)

.travis.yml

@@ -34,6 +34,8 @@ script:
   # test library examples with PlatformIO
   - pip install -U https://github.com/platformio/platformio/archive/develop.zip
   - platformio platform install https://github.com/platformio/platform-espressif32.git#feature/stage
+  - sed -i 's/https:\/\/github\.com\/espressif\/arduino-esp32\.git/*/' ~/.platformio/platforms/espressif32_stage/platform.json
+  - ln -s $TRAVIS_BUILD_DIR ~/.platformio/packages/framework-arduinoespressif32
   - "python -c \"import glob,subprocess,sys; map(lambda p: (sys.stdout.write('Library example: %s\\n' % p), subprocess.call(['pio', 'ci', p, '--board', 'esp32dev'])), glob.glob('libraries/*/examples/*/'))\""
 
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