Move activerecord dependency into gemspec (#220)

Moves dependencies from Gemfile into gemspec file. Makes the dependency
on activesupport explicit.

Author: drwl

Gemfile

@@ -2,15 +2,17 @@
 
 source "https://rubygems.org"
 
-gem "activerecord", require: false
+gemspec
+
 gem "rake"
-gem "rspec"
 
 group :development, :test do
   gem "aruba", "~> 2.1.0", require: false
   gem "byebug"
   gem "guard-rspec", require: false
 
+  gem "rspec"
+
   gem "standard", "~> 1.29.0"
   gem "terminal-notifier-guard", require: false
 
@@ -19,5 +21,3 @@ group :development, :test do
     gem "pry-byebug", require: false
   end
 end
-
-gemspec

annotaterb.gemspec

@@ -24,4 +24,7 @@ Gem::Specification.new do |spec|
   spec.bindir = "exe"
   spec.executables = Dir["exe/*"].map { |exe| File.basename(exe) }
   spec.require_paths = ["lib"]
+
+  spec.add_dependency "activerecord", ">= 6.0.0"
+  spec.add_dependency "activesupport", ">= 6.0.0"
 end