Conform constants to style guide

Constants should conform to style guide at https://solidity.readthedocs.io/en/latest/style-guide.html#constants

docs/contracts/constant-state-variables.rst

@@ -29,7 +29,7 @@ value types and strings.
     pragma solidity >=0.4.0 <0.7.0;
 
     contract C {
-        uint constant x = 32**22 + 8;
-        string constant text = "abc";
-        bytes32 constant myHash = keccak256("abc");
+        uint constant X = 32**22 + 8;
+        string constant TEXT = "abc";
+        bytes32 constant MY_HASH = keccak256("abc");
     }