Remove hard coded constant

Author: ianks

bundler/lib/bundler/templates/newgem/spec/newgem_spec.rb.tt

@@ -7,7 +7,7 @@ RSpec.describe <%= config[:constant_name] %> do
 
 <%- if config[:ext] == 'rust' -%>
   it "can call into Rust" do
-    result = Testing.hello("world")
+    result = <%= config[:constant_name] %>.hello("world")
 
     expect(result).to be("Hello earth, from Rust!")
   end

bundler/lib/bundler/templates/newgem/test/minitest/test_newgem.rb.tt

@@ -9,7 +9,7 @@ class <%= config[:minitest_constant_name] %> < Minitest::Test
 
 <%- if config[:ext] == 'rust' -%>
   def test_hello_world
-    assert_equal "Hello earth, from Rust!", Testing.hello("world")
+    assert_equal "Hello earth, from Rust!", <%= config[:constant_name] %>.hello("world")
   end
 <%- else -%>
   def test_it_does_something_useful