Fixed a problem with the 'ARDUINO_SDK_PATH' env variable format.

Bumped latest SDK version to 1.8.7 (Accidentally reverted back to 1.8.6 a few commits back).

Author: MrPointer

appveyor.yml

@@ -4,8 +4,9 @@ environment:
   MINGW_PATH: C:\mingw-w64\x86_64-7.2.0-posix-seh-rt_v5-rev1\mingw64\bin
   matrix:
   - ARDUINO_SDK_VERSION: 1.8.2
-  - ARDUINO_SDK_VERSION: 1.8.6
-  ARDUINO_SDK_PATH: $pwd\arduino-sdk\arduino-$env:ARDUINO_SDK_VERSION
+    ARDUINO_SDK_PATH: $pwd\arduino-sdk\arduino-1.8.2
+  - ARDUINO_SDK_VERSION: 1.8.7
+    ARDUINO_SDK_PATH: $pwd\arduino-sdk\arduino-1.8.7
 cache:
 - '%ARDUINO_SDK_PATH%'
 install: