In SystemCommand, fix success? and exit_status

When invoking a `SystemCommand` with `:must_succeed => false`, the `SystemCommand::Result` class would mistake a `Process.Status` object for a `Fixnum`.

This commit fixes this by instantiating `Result` with the actual status code as a number.

lib/cask/system_command.rb

@@ -28,11 +28,11 @@ def self.run(executable, options={})
     raw_stderr.close_read
 
     # Ruby 1.8 sets $?. Ruby 1.9+ has raw_wait_thr, and does not set $?.
-    processed_exit_status = raw_wait_thr.nil? ? $? : raw_wait_thr.value
+    processed_status = raw_wait_thr.nil? ? $? : raw_wait_thr.value
 
-    _assert_success(processed_exit_status, command, processed_stdout) if options[:must_succeed]
+    _assert_success(processed_status, command, processed_stdout) if options[:must_succeed]
 
-    Cask::SystemCommand::Result.new(command, processed_stdout, processed_stderr, processed_exit_status)
+    Cask::SystemCommand::Result.new(command, processed_stdout, processed_stderr, processed_status.exitstatus)
   end
 
   def self.run!(command, options={})

test/cask/system_command_test.rb

@@ -24,7 +24,7 @@
   describe "when the exit code is 1" do
     before do
       # See: https://bugs.ruby-lang.org/issues/1287
-      skip("Ruby 1.8.7 doesn’t see exit statuses") if TestHelper.ruby18?
+      skip("Ruby 1.8.7 doesn't see exit statuses") if TestHelper.ruby18?
     end
 
     describe "and the command must succeed" do