Proper loser handling in approval election. (#3392)

* Fix how we treat loser candidates.

* Bump.

* Improve doc.

* Update srml/elections/src/lib.rs

* Fix test

substrate/node/runtime/src/lib.rs

@@ -81,7 +81,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
 	spec_version: 146,
-	impl_version: 146,
+	impl_version: 147,
 	apis: RUNTIME_API_VERSIONS,
 };