make sure we use a pg gem version compatible with AR

jkraemer · jkraemer · commit aa7a09eda6ee · 2018-05-30T12:50:09.000+08:00
diff --git a/Gemfile b/Gemfile
@@ -5,5 +5,5 @@ gem 'immutable-struct'
 gem "rgeo"
 gem "rgeo-geojson"
 gem "rgeo-activerecord"
-gem "pg"
+gem "pg", "~> 0.15" # make sure we use a version compatible with AR
 gem 'activerecord-postgis-adapter', '~> 3.1'
