Bump prometheus-client-mmap to 0.9.4

Fixes failing builds with gcc on Archlinux and Ruby 2.4.4.

See https://gitlab.com/gitlab-org/prometheus-client-mmap/merge_requests/26
for more details.

Gemfile

@@ -306,7 +306,7 @@ group :metrics do
   gem 'influxdb', '~> 0.2', require: false
 
   # Prometheus
-  gem 'prometheus-client-mmap', '~> 0.9.3'
+  gem 'prometheus-client-mmap', '~> 0.9.4'
   gem 'raindrops', '~> 0.18'
 end
 

Gemfile.lock

@@ -635,7 +635,7 @@ GEM
       parser
       unparser
     procto (0.0.3)
-    prometheus-client-mmap (0.9.3)
+    prometheus-client-mmap (0.9.4)
     pry (0.10.4)
       coderay (~> 1.1.0)
       method_source (~> 0.8.1)
@@ -1126,7 +1126,7 @@ DEPENDENCIES
   peek-sidekiq (~> 1.0.3)
   pg (~> 0.18.2)
   premailer-rails (~> 1.9.7)
-  prometheus-client-mmap (~> 0.9.3)
+  prometheus-client-mmap (~> 0.9.4)
   pry-byebug (~> 3.4.1)
   pry-rails (~> 0.3.4)
   rack-attack (~> 4.4.1)

Gemfile.rails5.lock

@@ -639,7 +639,7 @@ GEM
       parser
       unparser
     procto (0.0.3)
-    prometheus-client-mmap (0.9.3)
+    prometheus-client-mmap (0.9.4)
     pry (0.10.4)
       coderay (~> 1.1.0)
       method_source (~> 0.8.1)
@@ -1136,7 +1136,7 @@ DEPENDENCIES
   peek-sidekiq (~> 1.0.3)
   pg (~> 0.18.2)
   premailer-rails (~> 1.9.7)
-  prometheus-client-mmap (~> 0.9.3)
+  prometheus-client-mmap (~> 0.9.4)
   pry-byebug (~> 3.4.1)
   pry-rails (~> 0.3.4)
   rack-attack (~> 4.4.1)