Replace links to readthedocs.io with ones using the new domain

docs/using-the-compiler.rst

@@ -441,7 +441,7 @@ Output Description
           // If the language used has no contract names, this field should equal to an empty string.
           "ContractName": {
             // The Ethereum Contract ABI. If empty, it is represented as an empty array.
-            // See https://solidity.readthedocs.io/en/develop/abi-spec.html
+            // See https://docs.soliditylang.org/en/develop/abi-spec.html
             "abi": [],
             // See the Metadata Output documentation (serialised JSON string)
             "metadata": "{...}",