Fix spelling of *modify*

lib/capybara.rb

@@ -117,7 +117,7 @@ module Capybara
     # For example modifying the :button selector to also find divs styled
     # to look like buttons might look like this
     #
-    #     Capybara.modfiy_selector(:button) do
+    #     Capybara.modify_selector(:button) do
     #       xpath { |locator| XPath::HTML.button(locator).or(XPath::css('div.btn')[XPath::string.n.is(locator)]) }
     #     end
     #

spec/selector_spec.rb

@@ -29,7 +29,7 @@ RSpec.describe Capybara do
       end
     end
 
-    describe "modfiy_selector" do
+    describe "modify_selector" do
       it "allows modifying a selector" do
         el = string.find(:custom_selector, 'a')
         expect(el.tag_name).to eq 'div'