Arduino Micro "Keyboard Not Found"
Based on the documentation :    


  These core libraries allow a 32u4 based boards or Due and Zero board to appear as a native Mouse and/or Keyboard to a connected computer.    


Core libraries (such as Keyboard.h) are not availabe if your board doesn't mentioned.

I don't know which one is right, since your question title mentioned "Arduino Micro" while at the end of your question, the board is "Arduino Uno".

Just for further information, Arduino Uno is based on - ATmega328P, and Arduino Micro is based on - ATmega32U4. So sure, that "hello world" program will works on Arduino Micro, but not on Arduino Uno.