Upgrade pg gem to 1.0 (#328)

This references #298. The rationale behind the changes:

* msgpack supports Ruby 2.5 on Windows starting from 1.2.4
* pg supports Ruby 2.5 on Windows starting from 1.0
* stackprof is Linux/OSX only

Gemfile

@@ -60,7 +60,7 @@ gem "octokit", "~> 4.8"
 gem "omniauth", "~> 1.8"
 gem "omniauth-github", "~> 1.3"
 gem "omniauth-twitter", "~> 1.4"
-gem "pg", "~> 0.21"
+gem "pg", "~> 1.0"
 gem "pry", "~> 0.11"
 gem "pry-rails", "~> 0.3"
 gem "puma", "~> 3.11"
@@ -142,7 +142,7 @@ group :test do
   gem "shoulda-matchers", "~> 3.1", require: false
   gem "simplecov", "~> 0.16", require: false
   gem "sinatra", "~> 2.0"
-  gem "stackprof", "~> 0.2", require: false
+  gem "stackprof", "~> 0.2", require: false, platforms: :ruby
   gem "stripe-ruby-mock", "~> 2.5", require: "stripe_mock"
   gem "test-prof", "~> 0.5"
   gem "timecop", "~> 0.9"

Gemfile.lock

@@ -569,7 +569,7 @@ GEM
     minitest (5.11.3)
     momentjs-rails (2.17.1)
       railties (>= 3.1)
-    msgpack (1.2.2)
+    msgpack (1.2.4)
     multi_json (1.13.1)
     multi_xml (0.6.0)
     multipart-post (2.0.0)
@@ -615,7 +615,7 @@ GEM
       parallel
     parser (2.5.1.2)
       ast (~> 2.4.0)
-    pg (0.21.0)
+    pg (1.0.0)
     powerpack (0.1.2)
     pry (0.11.3)
       coderay (~> 1.1.0)
@@ -979,7 +979,7 @@ DEPENDENCIES
   omniauth-github (~> 1.3)
   omniauth-twitter (~> 1.4)
   parallel_tests (~> 2.21)
-  pg (~> 0.21)
+  pg (~> 1.0)
   pry (~> 0.11)
   pry-rails (~> 0.3)
   puma (~> 3.11)