I am dumb and can't spell (#1366)

* rename implementor's guide to implementer's guide

* fix typos in more places

polkadot/.gitlab-ci.yml

@@ -195,7 +195,7 @@ generate-impl-guide:
     name: michaelfbryan/mdbook-docker-image:latest
     entrypoint: [""]
   script:
-    - mdbook build roadmap/implementors-guide
+    - mdbook build roadmap/implementers-guide
 
 .publish-build:                    &publish-build
   stage:                           publish

polkadot/availability-store/src/worker.rs

@@ -531,7 +531,7 @@ impl Worker {
 	}
 }
 
-/// Implementor of the [`BlockImport`] trait.
+/// Implementer of the [`BlockImport`] trait.
 ///
 /// Used to embed `availability-store` logic into the block imporing pipeline.
 ///

polkadot/node/overseer/src/lib.rs

@@ -17,7 +17,7 @@
 //! # Overseer
 //!
 //! `overseer` implements the Overseer architecture described in the
-//! [implementors-guide](https://github.com/paritytech/polkadot/blob/master/roadmap/implementors-guide/guide.md).
+//! [implementers-guide](https://github.com/paritytech/polkadot/blob/master/roadmap/implementers-guide/guide.md).
 //! For the motivations behind implementing the overseer itself you should
 //! check out that guide, documentation in this crate will be mostly discussing
 //! technical stuff.

polkadot/roadmap/implementors-guide/README.md → polkadot/roadmap/implementers-guide/README.md

@@ -4,6 +4,6 @@ The implementers' guide is compiled from several source files with [mdBook](http
 
 ```sh
 cargo install mdbook mdbook-linkcheck mdbook-graphviz
-mdbook serve roadmap/implementors-guide
+mdbook serve roadmap/implementers-guide
 open http://localhost:3000
 ```

polkadot/roadmap/implementors-guide/src/README.md → polkadot/roadmap/implementers-guide/src/README.md

 # Preamble
 
-This document aims to describe the purpose, functionality, and implementation of a host for Polkadot's _parachains_. It is not for the implementor of a specific parachain but rather for the implementor of the Parachain Host, which provides security and advancement for constituent parachains. In practice, this is for the implementors of Polkadot.
+This document aims to describe the purpose, functionality, and implementation of a host for Polkadot's _parachains_. It is not for the implementer of a specific parachain but rather for the implementer of the Parachain Host, which provides security and advancement for constituent parachains. In practice, this is for the implementers of Polkadot.
 
 There are a number of other documents describing the research in more detail. All referenced documents will be linked here and should be read alongside this document for the best understanding of the full picture. However, this is the only document which aims to describe key aspects of Polkadot's particular instantiation of much of that research down to low-level technical details and software architecture.