patch 8.1.0094: help text "usage:" is not capatalized

Problem:    Help text "usage:" is not capatalized.
Solution:   Make it "Usage:". (closes #3044)
diff --git a/src/main.c b/src/main.c
index c741fc4..66b67b8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3269,7 +3269,7 @@
 #endif
 
     mch_msg(longVersion);
-    mch_msg(_("\n\nusage:"));
+    mch_msg(_("\n\nUsage:"));
     for (i = 0; ; ++i)
     {
 	mch_msg(_(" vim [arguments] "));