fix typo in torchx doc (meta-pytorch#1104) (meta-pytorch#1104)

Summary:
Fix typo in torchx doc

Pull Request resolved: meta-pytorch#1104

Test Plan:
Imported from GitHub, without a `Test Plan:` line.

Rollback Plan:

Reviewed By: kiukchung

Differential Revision: D80435072

Pulled By: 610lyn

Author: 610lyn

torchx/runner/config.py

@@ -73,7 +73,7 @@
 
 #. In addition, it is possible to specify a different config other than .torchxconfig to
    load at runtime. Requirements are that the config path is specified by enviornment
-   variable TORCHX_CONFIG. It also disables hierarchy loading configs from multiple
+   variable TORCHXCONFIG. It also disables hierarchy loading configs from multiple
    directories as the cases otherwise.
 
 #. User level .torchxconfig