take the working revision of esp32 env

.travis.yml

@@ -22,7 +22,9 @@ install:
   - cp -R /usr/local/share/arduino/OpenMQTTGateway/lib/. /usr/local/share/arduino/libraries
   - mkdir -p /usr/local/share/arduino/hardware/espressif
   - cd /usr/local/share/arduino/hardware/espressif
-  - git clone https://github.com/espressif/arduino-esp32.git esp32
+  - wget https://github.com/espressif/arduino-esp32/archive/a153f6ad280e5932be9c80341556348ff505d586.zip -O /tmp/esp32.zip
+  - unzip /tmp/esp32.zip -d /usr/local/share/arduino/hardware/espressif
+  - mv arduino-esp32* esp32
   - cd esp32/tools/
   - python get.py
   - cd /usr/local/share/arduino/OpenMQTTGateway