PlatformIO build issue in linux

[nitin710]

• When building the Emotibit firmware on linux without downloading Arduino IDE, the compiler throws error stating cannot find String.h file
• The places where the compiler throws the errors are
  • https://github.com/EmotiBit/EmotiBit_XPlat_Utils/blob/37e13bd6beb804d83a820e4a99adf12c5598248c/src/EmotiBitPacket.h#L5
  • https://github.com/EmotiBit/EmotiBit_XPlat_Utils/blob/37e13bd6beb804d83a820e4a99adf12c5598248c/src/EmotiBitEdaCalibration.h#L33
• Commenting out these #includes compiles the code as expected.

Further investigation needed.