update Gemfile sample code

Amend the sample Gemfile code to specify version ~>0.3.0.
Remove unnecessary require option from sample Gemfile code.

Author: fig

README.md

@@ -8,7 +8,7 @@ A ruby library/gem for interacting with `.docx` files. currently capabilities in
 
 Requires ruby (tested with 2.1.1)
 
-    gem 'docx', '~> 0.2.07', :require => ["docx"]
+    gem 'docx', '~> 0.3.0'
 
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