Fix docblock syntax

contracts/token/StandardToken.sol

@@ -66,7 +66,7 @@ contract StandardToken is ERC20, BasicToken {
     return allowed[_owner][_spender];
   }
   
-    /*
+  /**
    * approve should be called when allowed[_spender] == 0. To increment
    * allowed value is better to use this function to avoid 2 calls (and wait until 
    * the first transaction is mined)