Run CI only on Python 3

Author: valeros

.github/workflows/examples.yml

@@ -8,7 +8,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-16.04, windows-latest, macos-latest]
-        python-version: [2.7, 3.7]
+        python-version: [3.7]
         example:
           - "examples/mbed-rtos-blink-baremetal"
           - "examples/mbed-rtos-blockdevice"