remove references to the nursery

Last part of #171

.github/workflows/main.yml

@@ -17,7 +17,7 @@ jobs:
     - name: Install mdbook
       run: |
         mkdir bin
-        curl -sSL https://github.com/rust-lang-nursery/mdBook/releases/download/v0.3.4/mdbook-v0.3.4-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
+        curl -sSL https://github.com/rust-lang/mdBook/releases/download/v0.3.4/mdbook-v0.3.4-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
         echo "##[add-path]$(pwd)/bin"
     - name: Report versions
       run: |

README.md

@@ -23,7 +23,7 @@ infinitesimal fragments of despair.
 
 Building the Nomicon requires [mdBook]. To get it:
 
-[mdBook]: https://github.com/rust-lang-nursery/mdBook
+[mdBook]: https://github.com/rust-lang/mdBook
 
 ```bash
 $ cargo install mdbook