remove runtime dependency on slop ~> v3.4, fix specs that depended on it

pry.gemspec

@@ -19,7 +19,6 @@ Gem::Specification.new do |s|
   s.files         = `git ls-files bin lib *.md LICENSE`.split("\n")
 
   s.add_dependency 'coderay',       '~> 1.1.0'
-  s.add_dependency 'slop',          '~> 3.4'
   s.add_dependency 'method_source', '~> 0.8.1'
   s.add_development_dependency 'bundler', '~> 1.0'
 end

spec/commands/gem_list_spec.rb

@@ -7,13 +7,12 @@ describe "gem-list" do
 
   it 'should work arglessly' do
     list = pry_eval('gem-list')
-    expect(list).to match(/slop \(/)
     expect(list).to match(/rspec \(/)
   end
 
   it 'should find arg' do
-    prylist = pry_eval('gem-list slop')
-    expect(prylist).to match(/slop \(/)
+    prylist = pry_eval('gem-list method_source')
+    expect(prylist).to match(/method_source \(/)
     expect(prylist).not_to match(/rspec/)
   end