Update gemfile so jruby rake build build -java gem and MRI rake build creates MRI gem

Update gemfile so jruby rake build build -java gem and MRI rake build creates MRI gem

diff --git a/mini_sql.gemspec b/mini_sql.gemspec
index bd0f8ed..523baa4 100644
--- a/mini_sql.gemspec
+++ b/mini_sql.gemspec
@@ -15,6 +15,8 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://discourse.org"
   spec.license       = "MIT"
 
+  spec.platform = 'java' if RUBY_ENGINE == 'jruby'
+
   # Specify which files should be added to the gem when it is released.
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
   spec.files         = Dir.chdir(File.expand_path('..', __FILE__)) do
@@ -25,9 +27,14 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "bundler", "> 1.16"
   spec.add_development_dependency "rake", "~> 10.0"
   spec.add_development_dependency "minitest", "~> 5.0"
-  spec.add_development_dependency "pg", "> 1"
   spec.add_development_dependency "guard", "~> 2.14"
   spec.add_development_dependency "guard-minitest", "~> 2.4"
   spec.add_development_dependency "activesupport", "~> 5.2"
-  spec.add_development_dependency "sqlite3", "~> 1.3"
+
+  if RUBY_ENGINE == 'jruby'
+    spec.add_development_dependency "activerecord-jdbcpostgresql-adapter", "~> 52.2"
+  else
+    spec.add_development_dependency "pg", "> 1"
+    spec.add_development_dependency "sqlite3", "~> 1.3"
+  end
 end

GitHub sha: d3ec634f