Merge pull request #6847 from ethereum/style-fixes-libraries

[DOCS] Make libraries code examples conform to style guide

docs/contracts/libraries.rst

@@ -49,6 +49,7 @@ more advanced example to implement a set).
 
     pragma solidity >=0.4.22 <0.7.0;
 
+
     library Set {
         // We define a new struct datatype that will be used to
         // hold its data in the calling contract.
@@ -89,6 +90,7 @@ more advanced example to implement a set).
         }
     }
 
+
     contract C {
         Set.Data knownValues;