RefCell::get_mut: fix typo

and fix the same typo in a bunch of other places

clippy_dev/src/setup/git_hook.rs

@@ -6,7 +6,7 @@
 /// Rusts setup uses `git rev-parse --git-common-dir` to get the root directory of the repo.
 /// I've decided against this for the sake of simplicity and to make sure that it doesn't install
 /// the hook if `clippy_dev` would be used in the rust tree. The hook also references this tool
-/// for formatting and should therefor only be used in a normal clone of clippy
+/// for formatting and should therefore only be used in a normal clone of clippy
 const REPO_GIT_DIR: &str = ".git";
 const HOOK_SOURCE_FILE: &str = "util/etc/pre-commit.sh";
 const HOOK_TARGET_FILE: &str = ".git/hooks/pre-commit";

clippy_utils/src/hir_utils.rs

@@ -113,7 +113,7 @@ pub fn eq_stmt(&mut self, left: &Stmt<'_>, right: &Stmt<'_>) -> bool {
                     }
                 }
 
-                // eq_pat adds the HirIds to the locals map. We therefor call it last to make sure that
+                // eq_pat adds the HirIds to the locals map. We therefore call it last to make sure that
                 // these only get added if the init and type is equal.
                 both(&l.init, &r.init, |l, r| self.eq_expr(l, r))
                     && both(&l.ty, &r.ty, |l, r| self.eq_ty(l, r))