simplify and improve git ignore rules

Using a pattern to match the source tar.gz files prevents fedpkg upload
from needlessly appending each new source file to .gitignore.

Also ignore expanded source directories.

.gitignore

@@ -1,16 +1,2 @@
-ncdu-1.6.tar.gz
+/ncdu-*/
-/ncdu-1.7.tar.gz
+/ncdu-*.tar.gz*
-/ncdu-1.8.tar.gz
-/ncdu-1.9.tar.gz
-/ncdu-1.10.tar.gz
-/ncdu-1.11.tar.gz
-/ncdu-1.12.tar.gz
-/ncdu-1.13.tar.gz
-/ncdu-1.14.tar.gz
-/ncdu-1.14.1.tar.gz
-/ncdu-1.14.2.tar.gz
-/ncdu-1.15.tar.gz
-/ncdu-1.15.1.tar.gz
-/ncdu-1.16.tar.gz
-/ncdu-1.17.tar.gz
-/ncdu-1.18.tar.gz