Pin gem dependencies

So that we can more selectively update them
in the future.

Gemfile.lock

@@ -2,14 +2,14 @@ PATH
   remote: .
   specs:
     gitlab-exporter (10.3.0)
-      connection_pool (~> 2.2.1)
-      pg (~> 1.1)
-      puma (~> 5.3.2)
-      quantile (~> 0.2.0)
-      redis (~> 4.1.2)
-      redis-namespace (~> 1.6.0)
-      sidekiq (~> 5.2.1)
-      sinatra (~> 2.0.4)
+      connection_pool (= 2.2.5)
+      pg (= 1.2.3)
+      puma (= 5.3.2)
+      quantile (= 0.2.1)
+      redis (= 4.1.4)
+      redis-namespace (= 1.6.0)
+      sidekiq (= 5.2.9)
+      sinatra (= 2.0.8.1)
 
 GEM
   remote: https://rubygems.org/

gitlab-exporter.gemspec

@@ -20,14 +20,14 @@ Gem::Specification.new do |s|
   s.homepage      = "http://gitlab.com"
   s.license       = "MIT"
 
-  s.add_runtime_dependency "connection_pool", "~> 2.2.1"
-  s.add_runtime_dependency "pg", "~> 1.1"
-  s.add_runtime_dependency "puma", "~> 5.3.2"
-  s.add_runtime_dependency "quantile", "~> 0.2.0"
-  s.add_runtime_dependency "redis", "~> 4.1.2"
-  s.add_runtime_dependency "redis-namespace", "~> 1.6.0"
-  s.add_runtime_dependency "sidekiq", "~> 5.2.1"
-  s.add_runtime_dependency "sinatra", "~> 2.0.4"
+  s.add_runtime_dependency "connection_pool", "2.2.5"
+  s.add_runtime_dependency "pg", "1.2.3"
+  s.add_runtime_dependency "puma", "5.3.2"
+  s.add_runtime_dependency "quantile", "0.2.1"
+  s.add_runtime_dependency "redis", "4.1.4"
+  s.add_runtime_dependency "redis-namespace", "1.6.0"
+  s.add_runtime_dependency "sidekiq", "5.2.9"
+  s.add_runtime_dependency "sinatra", "2.0.8.1"
 
   s.add_development_dependency "rspec", "~> 3.7.0"
   s.add_development_dependency "rspec-expectations", "~> 3.7.0"