doc: add missing space in test/README.md

PR-URL: https://github.com/nodejs/node/pull/15278
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/README.md

@@ -16,7 +16,7 @@ On how to run tests in this directory, see
 |addons             |Yes            |Tests for [addon](https://nodejs.org/api/addons.html) functionality along with some tests that require an addon to function  properly.|
 |cctest             |Yes            |C++ test that is run as part of the build process.|
 |common             |               |Common modules shared among many tests. [Documentation](./common/README.md)|
-|debugger           |No             |Tests for [debugger](https://nodejs.org/api/debugger.html)functionality along with some tests that require an addon to function properly.|
+|debugger           |No             |Tests for [debugger](https://nodejs.org/api/debugger.html) functionality along with some tests that require an addon to function properly.|
 |fixtures           |               |Test fixtures used in various tests throughout the test suite.|
 |gc                 |No             |Tests for garbage collection related functionality.|
 |inspector          |Yes            |Tests for the V8 inspector integration.|