Merge branch '69-monotonic-clock' into 'master'

Support old versions of ruby without a monotonic clock

Closes #69

See merge request !161

CHANGELOG

+v5.8.1
+  - Support old versions of ruby without monotonic clock
+
 v5.8.0
   - Fix SSH support for Git for Windows v2.14
 

VERSION

-5.8.0
+5.8.1

lib/gitlab_metrics.rb

@@ -21,7 +21,11 @@ module GitlabMetrics
     #
     # Returns the time as a Fixnum.
     def self.monotonic_time
-      Process.clock_gettime(Process::CLOCK_MONOTONIC, :millisecond)
+      if defined?(Process::CLOCK_MONOTONIC)
+        Process.clock_gettime(Process::CLOCK_MONOTONIC, :millisecond)
+      else
+        Process.clock_gettime(Process::CLOCK_REALTIME, :millisecond)
+      end
     end
   end