fix case sensitivity problem
fix case sensitivity problem

See [this post](https://community.platformio.org/t/esp8266-12e-with-arduino-framework-build-error-esp8266wifi-h/328/20?u=boneskull) about the problem
JonSilver/ConfigManager,JonSilver/ConfigManager,nrwiersma/ConfigManager,nrwiersma/ConfigManager