Update Arduino core to v2.7.1

Resolves #742

Author: valeros

platform.json

@@ -93,7 +93,7 @@
       "owner": "platformio",
       "version": "~2.50501.0",
       "optionalVersions": [
-        "~2.50700.0"
+        "~2.50900.0"
       ]
     },
     "framework-cmsis-stm32f0": {
@@ -190,7 +190,7 @@
       "type": "framework",
       "optional": true,
       "owner": "platformio",
-      "version": "~4.20600.0"
+      "version": "~4.20701.0"
     },
     "framework-arduinoststm32-maple": {
       "type": "framework",

platform.py

@@ -49,7 +49,7 @@ def configure_default_packages(self, variables, targets):
                 self.packages["framework-arduinoststm32"]["optional"] = True
             else:
                 self.packages["toolchain-gccarmnoneeabi"]["version"] = "~1.120301.0"
-                self.packages["framework-cmsis"]["version"] = "~2.50700.0"
+                self.packages["framework-cmsis"]["version"] = "~2.50900.0"
                 self.packages["framework-cmsis"]["optional"] = False
 
         if "mbed" in frameworks: