skip generating gem file contents if this is not a git checkout

Author: busterb

metasploit-framework.gemspec

@@ -24,9 +24,11 @@ Gem::Specification.new do |spec|
   spec.homepage      = 'https://www.metasploit.com'
   spec.license       = 'BSD-3-clause'
 
-  spec.files         = `git ls-files`.split($/).reject { |file|
-    file =~ /^documentation|^data\/gui|^external/
-  }
+  if File.directory?(File.join(__FILE__, ".git"))
+    spec.files         = `git ls-files`.split($/).reject { |file|
+      file =~ /^documentation|^data\/gui|^external/
+    }
+  end
   spec.bindir = '.'
   if ENV['CREATE_BINSTUBS']
     spec.executables   = [