doc: fix mistyped "env flags" command

Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/doc/usage/cmd/env.rst b/doc/usage/cmd/env.rst
index a859e32..a7e2169 100644
--- a/doc/usage/cmd/env.rst
+++ b/doc/usage/cmd/env.rst
@@ -350,7 +350,7 @@
 exists
     CONFIG_CMD_ENV_EXISTS
 
-flsgs
+flags
     CONFIG_CMD_ENV_FLAGS
 
 erase