Fix typo as suggested by camelid

Author: jyn514

Diff for: src/building/bootstrapping.md

@@ -240,7 +240,7 @@ The `RUSTFLAGS_STAGE_0`, `RUSTFLAGS_STAGE_1` and `RUSTFLAGS_STAGE_2`
 environment variables pass the given flags when building stage 0, 1, and 2
 artifacts respectively.
 
-Additionally, the `RUSTFLAGS_STAGE_NOT_0` variable, as its name suggests, pass
+Additionally, the `RUSTFLAGS_STAGE_NOT_0` variable, as its name suggests, passes
 the given arguments if the stage is not 0.
 
 ## Environment Variables