Default to true when javascriptEnabled capability is not set

Mimics b31dc3f in Ruby so that drivers
that don't set javascriptEnabled to true explicitly (e.g. Edge) still
can execute scripts.

Closes #4651.

Author: p0deje

rb/lib/selenium/webdriver/remote/capabilities.rb

@@ -48,6 +48,15 @@ class Capabilities
           end
         end
 
+        #
+        # Returns javascript_enabled capability.
+        # It is true if not set explicitly.
+        #
+        def javascript_enabled
+          javascript_enabled = @capabilities.fetch(:javascript_enabled)
+          javascript_enabled.nil? ? true : javascript_enabled
+        end
+
         alias_method :css_selectors_enabled?, :css_selectors_enabled
         alias_method :javascript_enabled?, :javascript_enabled
         alias_method :native_events?, :native_events

rb/spec/unit/selenium/webdriver/remote/capabilities_spec.rb

@@ -94,6 +94,11 @@ module Remote
           expect(capabilities_hash).not_to have_key('proxy')
         end
 
+        it 'should default to javascript enabled if it is not explicitly defined' do
+          capabilities = Capabilities.new(javascript_enabled: nil)
+          expect(capabilities.javascript_enabled).to eq(true)
+        end
+
         it 'can merge capabilities' do
           a = Capabilities.chrome
           b = Capabilities.htmlunit