patch 8.1.1955: tests contain typos

Problem:    Tests contain typos.
Solution:   Correct the typos. (Dominique Pelle)
diff --git a/src/testdir/popupbounce.vim b/src/testdir/popupbounce.vim
index 2d1345b..b9f7bd1 100644
--- a/src/testdir/popupbounce.vim
+++ b/src/testdir/popupbounce.vim
@@ -6,7 +6,7 @@
 "    ./vim --clean -S testdir/popupbounce.vim main.c
 "    gprof vim gmon.out | vim -
 
-" using line contination
+" using line continuation
 set nocp
 
 " don't switch screens when quitting, so we can read the frames/sec