Update package_sparkfun_index.json

Author: awende

IDE_Board_Manager/package_sparkfun_index.json

@@ -2084,7 +2084,7 @@
           "architecture": "stm32",
           "version": "1.0.0",
           "category": "Contributed",
-          "url": "https://github.com/sparkfun/Arduino_Boards/raw/STM32_testing/IDE_Board_Manager/sparkfun-stm32-1.0.0.tar.bz2",
+          "url": "https://github.com/sparkfun/Arduino_Boards/raw/master/IDE_Board_Manager/sparkfun-stm32-1.0.0.tar.bz2",
           "archiveFileName": "sparkfun-stm32-1.0.0.tar.bz2",
           "checksum": "SHA-256:2ea9f35f66fbb73b26698319f202391b525d1cceb7a8fe2be454e89dc6e5b922",
           "size": "4982552",