docs: Fix formatting of GCE_METADATA_HOST (#890)

* Clean docs up

* Update google/auth/environment_vars.py

Co-authored-by: arithmetic1728 <58957152+arithmetic1728@users.noreply.github.com>

google/auth/environment_vars.py

@@ -41,15 +41,17 @@
 # These two variables allow for customization of the addresses used when
 # contacting the GCE metadata service.
 GCE_METADATA_HOST = "GCE_METADATA_HOST"
-GCE_METADATA_ROOT = "GCE_METADATA_ROOT"
 """Environment variable providing an alternate hostname or host:port to be
 used for GCE metadata requests.
 
-This environment variable is originally named GCE_METADATA_ROOT. System will
-check the new variable first; should there be no value present,
-the system falls back to the old variable.
+This environment variable was originally named GCE_METADATA_ROOT. The system will
+check this environemnt variable first; should there be no value present,
+the system will fall back to the old variable.
 """
 
+GCE_METADATA_ROOT = "GCE_METADATA_ROOT"
+"""Old environment variable for GCE_METADATA_HOST."""
+
 GCE_METADATA_IP = "GCE_METADATA_IP"
 """Environment variable providing an alternate ip:port to be used for ip-only
 GCE metadata requests."""