[mutter] main: Fix typo

[Florian Müllner <fmuellner src gnome org>]

commit 33c2a38ff7ce22f5e6f202ba1a3289eff61787fe
Author: Florian Müllner <fmuellner gnome org>
Date:   Fri May 4 20:15:06 2018 +0200

    main: Fix typo

 src/core/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/core/main.c b/src/core/main.c
index be7a90feb..a9548f728 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -417,7 +417,7 @@ check_for_wayland_session_type (void)
  *
  * If no flag is passed that forces the compositor type, the compositor type
  * is determined first from the logind session type, or if that fails, from the
- * XDG_SESSION_TYPE enviornment variable.
+ * XDG_SESSION_TYPE environment variable.
  *
  * If no flag is passed that forces the backend type, the backend type is
  * determined given the compositor type. If the compositor is a Wayland