DOC: Incorrect environment variable description
The `NUM_BUILD_JOBS` environment variable had a redundant `CUPY_` prepended to it in the docs.
@@ -101,7 +101,7 @@ These environment variables are used during installation (building CuPy from sou
| | architectures in build time. When this is not set, |
| | the default is to support all architectures. |
+------------------------------+----------------------------------------------------------------+
-| ``CUPY_CUPY_NUM_BUILD_JOBS`` | To enable or disable parallel build, sets the number of |
+| ``CUPY_NUM_BUILD_JOBS`` | To enable or disable parallel build, sets the number of |
| | processes used to build the extensions in parallel. Defaults |
| | to ``4`` |
+------------------------------+----------------------------------------------------------------+
