fix Pausable documentation

contracts/lifecycle/Pausable.sol

@@ -16,7 +16,7 @@ contract Pausable is Ownable {
 
 
   /**
-   * @dev modifier to allow actions only when the contract IS paused
+   * @dev Modifier to make a function callable only when the contract is not paused.
    */
   modifier whenNotPaused() {
     require(!paused);
@@ -24,7 +24,7 @@ contract Pausable is Ownable {
   }
 
   /**
-   * @dev modifier to allow actions only when the contract IS NOT paused
+   * @dev Modifier to make a function callable only when the contract is paused.
    */
   modifier whenPaused() {
     require(paused);