Merge pull request #2498 from rust-lang/tshepang-patch-1

add missing word

Author: Noratrieb

src/doc/rustc-dev-guide/src/tests/misc.md

@@ -9,7 +9,7 @@ for testing:
 
 - `RUSTC_BOOTSTRAP=1` will "cheat" and bypass usual stability checking, allowing
   you to use unstable features and cli flags on a stable `rustc`.
-- `RUSTC_BOOTSTRAP=-1` will force a given `rustc` to pretend that is a stable
+- `RUSTC_BOOTSTRAP=-1` will force a given `rustc` to pretend it is a stable
   compiler, even if it's actually a nightly `rustc`. This is useful because some
   behaviors of the compiler (e.g. diagnostics) can differ depending on whether
   the compiler is nightly or not.