mac: Bump the deployment target of gcapi_lib to 10.5.

The code requires methods only present on 10.5+, so having a deployment target
of 10.4 is incorrect.

BUG=471823

Review URL: https://codereview.chromium.org/1112753002

Cr-Commit-Position: refs/heads/master@{#327543}

chrome/chrome_installer.gypi

@@ -1047,7 +1047,7 @@
           },
           'xcode_settings': {
             'ARCHS': [ 'i386', 'x86_64' ],
-            'MACOSX_DEPLOYMENT_TARGET': '10.4',
+            'MACOSX_DEPLOYMENT_TARGET': '10.5',
             'GCC_ENABLE_OBJC_GC': 'supported',
           },
         },