change the min mac os x version required.

It fixes an issue when running `npm install` for a project with *Node
v6.11.5* and *npm v3.10.10* on *Mac OS X 10.4 Mojave* and *Xcode v9.4.1
|| Xcode v10.0*. It asks for the 'utility' file when running
`node-gyp rebuild`.

Fixes: nodejs/node-gyp#1574

Author: Alejandro Ventura Contreras

common.gypi

@@ -367,7 +367,7 @@
           'GCC_ENABLE_PASCAL_STRINGS': 'NO',        # No -mpascal-strings
           'GCC_THREADSAFE_STATICS': 'NO',           # -fno-threadsafe-statics
           'PREBINDING': 'NO',                       # No -Wl,-prebind
-          'MACOSX_DEPLOYMENT_TARGET': '10.7',       # -mmacosx-version-min=10.7
+          'MACOSX_DEPLOYMENT_TARGET': '10.9',       # -mmacosx-version-min=10.9
           'USE_HEADERMAP': 'NO',
           'OTHER_CFLAGS': [
             '-fno-strict-aliasing',