Update regex for extracting Xcode version (#302)

Author: dsiher

libraries/command_line_tools.rb

@@ -60,7 +60,7 @@ def enable_install_on_demand
     end
 
     def xcode_version(product)
-      product.match(/Xcode.{0,20}-(?<version>\d+\.\d+)/)['version']
+      product.match(/Xcode.{0,20}-(?<version>\d+\.\d+(?:\.\d+)?)/)['version']
     end
 
     def macos_version