Bump prometheus client version

Gemfile.lock

@@ -561,7 +561,7 @@ GEM
     premailer-rails (1.9.2)
       actionmailer (>= 3, < 6)
       premailer (~> 1.7, >= 1.7.9)
-    prometheus-client-mmap (0.7.0.beta1)
+    prometheus-client-mmap (0.7.0.beta3)
       quantile (~> 0.2.0)
     pry (0.10.4)
       coderay (~> 1.1.0)
@@ -1000,7 +1000,7 @@ DEPENDENCIES
   pg (~> 0.18.2)
   poltergeist (~> 1.9.0)
   premailer-rails (~> 1.9.0)
-  prometheus-client-mmap (~> 0.7.0.beta1)
+  prometheus-client-mmap
   pry-byebug (~> 3.4.1)
   pry-rails (~> 0.3.4)
   rack-attack (~> 4.4.1)