compiletest: fix outdated rustdoc-js test suite name

Author: jieyouxu

Diff for: src/tests/directives.md

@@ -248,7 +248,7 @@ Consider writing the test as a proper incremental test instead.
 
 | Directive   | Explanation                                                  | Supported test suites                    | Possible values           |
 |-------------|--------------------------------------------------------------|------------------------------------------|---------------------------|
-| `doc-flags` | Flags passed to `rustdoc` when building the test or aux file | `rustdoc`, `js-doc-test`, `rustdoc-json` | Any valid `rustdoc` flags |
+| `doc-flags` | Flags passed to `rustdoc` when building the test or aux file | `rustdoc`, `rustdoc-js`, `rustdoc-json` | Any valid `rustdoc` flags |
 
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 **FIXME(rustdoc)**: what does `check-test-line-numbers-match` do?