Use the latest Arduino IDE version (espressif#66)

As of today, the latest Arduino IDE version is 1.8.11 which includes
several bug-fixes and enhancements.

Author: platisd

install.sh

@@ -43,7 +43,7 @@ echo "########################################################################";
 
 # if .travis.yml does not set version
 if [ -z $ARDUINO_IDE_VERSION ]; then
-export ARDUINO_IDE_VERSION="1.8.10"
+export ARDUINO_IDE_VERSION="1.8.11"
 echo "NOTE: YOUR .TRAVIS.YML DOES NOT SPECIFY ARDUINO IDE VERSION, USING $ARDUINO_IDE_VERSION"
 fi