patch 8.0.1548: screen dump test script not included in distribution

Problem:    Screen dump test script not included in distribution.
Solution:   Add the script to the list of distributed files.
diff --git a/Filelist b/Filelist
index 66d8336..928d963 100644
--- a/Filelist
+++ b/Filelist
@@ -110,6 +110,7 @@
 		src/testdir/sautest/autoload/*.vim \
 		src/testdir/runtest.vim \
 		src/testdir/shared.vim \
+		src/testdir/screendump.vim \
 		src/testdir/view_util.vim \
 		src/testdir/setup.vim \
 		src/testdir/gui_init.vim \