srml-contracts: Minor fixes to docs. (#3262)

* Adjust documentation.

* Bump impl_version.

* Update srml/contracts/src/wasm/runtime.rs

Co-Authored-By: Hero Bird <robbepop@web.de>

* Remove incorrect doc.

substrate/node/runtime/src/lib.rs

@@ -80,7 +80,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
 	spec_version: 127,
-	impl_version: 127,
+	impl_version: 128,
 	apis: RUNTIME_API_VERSIONS,
 };