Add printscreen as a special key mapping for 44

[ifdion]

Add printscreen as a special key mapping for 44

[coveralls]

Pull Request Test Coverage Report for Build 796

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 78.947%

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Totals
Change from base Build 731:	0.0%
Covered Lines:	191
Relevant Lines:	211

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💛 - Coveralls

[codecov-io]

Codecov Report

Merging #229 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #229   +/-   ##
=======================================
  Coverage   90.52%   90.52%           
=======================================
  Files           1        1           
  Lines         211      211           
=======================================
  Hits          191      191           
  Misses         20       20           

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[jaywcjlove]

@ifdion It is not a standard key code? macOS keyCode=124, windows keyCode=44, Linux keyCode=42 #217

KeyboardEvent.code	Internet Explorer 11	Google Chrome 34		Chromium 34	Safari 7	Gecko 29
	Windows	Windows	Mac (10.9)	Linux (Ubuntu 14.04)	Mac (10.9)	Windows	Mac (10.9)	Linux (Ubuntu 14.04)
"PrintScreen"	0x2C (44) *4	0x2C (44) *4	0x7C (124)*5	0x2A (42)	0x7C (124)*5	0x2C (44) *4	0x2C (44)	0x2A (42)

https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/keyCode

[ifdion]

@jaywcjlove You're right. Should we check the the value on the user agent as you did on isff?

[jaywcjlove]

@ifdion I wonder if there is a better way to achieve it?