Fix typos and markdown (#2388)

* Fix typos

* Align properly

* Update core/consensus/slots/src/lib.rs

Co-Authored-By: cmichi <mich@elmueller.net>

* Update core/network/src/test/mod.rs

Co-Authored-By: cmichi <mich@elmueller.net>

* Update core/finality-grandpa/src/communication/mod.rs

Co-Authored-By: cmichi <mich@elmueller.net>

* Update core/consensus/common/src/import_queue.rs

Co-Authored-By: cmichi <mich@elmueller.net>

substrate/core/network/src/test/mod.rs

@@ -58,7 +58,7 @@ pub use test_client::TestClient;
 pub struct PassThroughVerifier(pub bool);
 
 #[cfg(any(test, feature = "test-helpers"))]
-/// This Verifiyer accepts all data as valid
+/// This `Verifier` accepts all data as valid.
 impl<B: BlockT> Verifier<B> for PassThroughVerifier {
 	fn verify(
 		&self,