Use absolute module namespace to prevent conflict with Guard::Process

Guard has it's own Process class and when calling Process.kill will use the Process module/class under Guard which does not implement kill resulting in error like: NoMethodError: undefined method `wait2' for Guard::Process:Class.

CHANGELOG.md

@@ -1,12 +1,13 @@
 2.2.1 (Next)
 ============
 
+* [#24](https://github.com/dblock/guard-rack/pull/24): Use absolute module namespace to prevent conflict with Guard::Process - [@cristianbica](https://github.com/cristianbica).
 * Your contribution here.
 
 2.2.0 (4/16/2016)
 =================
 
-* [#23](https://github.com/dblock/guard-rack/pull/23) Added Windows support - [@jonyeezs](https://github.com/jonyeezs).
+* [#23](https://github.com/dblock/guard-rack/pull/23): Added Windows support - [@jonyeezs](https://github.com/jonyeezs).
 
 2.1.1 (03/07/2015)
 ============

lib/guard/rack/custom_process.rb

@@ -24,10 +24,10 @@ def kill(pid, force = false)
           result = -1
           UI.debug("Trying to kill Rack (PID #{pid})...")
           unless force
-            Process.kill('INT', pid)
+            ::Process.kill('INT', pid)
             begin
               Timeout.timeout(options[:timeout]) do
-                _, status = Process.wait2(pid)
+                _, status = ::Process.wait2(pid)
                 result = status.exitstatus
                 UI.debug("Killed Rack (Exit status: #{result})")
               end
@@ -36,7 +36,7 @@ def kill(pid, force = false)
               force = true
             end
           end
-          Process.kill('TERM', pid) if force
+          ::Process.kill('TERM', pid) if force
           result
         end
       end