Properly bump prometheus-client-mmap gem versions

Only the Gemfile.lock was updated before.

Gemfile

@@ -283,7 +283,7 @@ group :metrics do
   gem 'influxdb', '~> 0.2', require: false
   # Prometheus
-  gem 'prometheus-client-mmap', '~> 0.7.0.beta39'
+  gem 'prometheus-client-mmap', '~> 0.7.0.beta43'
   gem 'raindrops', '~> 0.18'
 end

Gemfile.lock

@@ -1113,7 +1113,7 @@ DEPENDENCIES
   peek-sidekiq (~> 1.0.3)
   pg (~> 0.18.2)
   premailer-rails (~> 1.9.7)
-  prometheus-client-mmap (~> 0.7.0.beta39)
+  prometheus-client-mmap (~> 0.7.0.beta43)
   pry-byebug (~> 3.4.1)
   pry-rails (~> 0.3.4)
   rack-attack (~> 4.4.1)