go: Update test string for mounttable_test

Fixed a typo

Change-Id: I0c67fafdf7e426800f307ee331fedad8a46b71b1
diff --git a/services/mounttable/mounttablelib/mounttable_test.go b/services/mounttable/mounttablelib/mounttable_test.go
index 7cfbf17..6d6175c 100644
--- a/services/mounttable/mounttablelib/mounttable_test.go
+++ b/services/mounttable/mounttablelib/mounttable_test.go
@@ -57,7 +57,7 @@
 		if !shouldSucceed {
 			return
 		}
-		boom(t, "Failed to Mount %s onto %s: %s", service, name, err)
+		boom(t, "Failed to Unmount %s off of %s: %s", service, name, err)
 	}
 }