Modify markdown-mode snippet to remove new line

Ryota0312 · Ryota0312 · commit a8647a86c50e · 2019-01-07T12:32:47.000+09:00
I think that it is more convenient for bullets not to put newlines.
diff --git a/snippets/markdown-mode/plus b/snippets/markdown-mode/plus
@@ -3,4 +3,4 @@
 # key: +
 # --
 + ${1:Text}
-+$0
++$0
