gyp: modify XcodeVersion() to convert "4.2" to "0420" and "10.0" to "1000"
gyp: modify XcodeVersion() to convert "4.2" to "0420" and "10.0" to "1000"

Ref: https://github.com/nodejs/node-addon-api/issues/445#issuecomment-535361389
PR-URL: https://github.com/nodejs/node-gyp/pull/1895
Reviewed-By: Rod Vagg <f9f03903429036ef609ed7ca822fddfa76155c29@vagg.org>

nodegit/node-gyp,nodejs/node-gyp,nodejs/node-gyp,nodejs/node-gyp,nodejs/node-gyp,nodejs/node-gyp,nodegit/node-gyp,nodegit/node-gyp,nodegit/node-gyp,nodegit/node-gyp