Captialize meta.description of all packages

In line with the Nixpkgs manual.

A mechanical change, done with this command:

  find pkgs -name "*.nix" | \
      while read f; do \
          sed -e 's/description\s*=\s*"\([a-z]\)/description = "\u\1/' -i "$f"; \
      done

I manually skipped some:

* Descriptions starting with an abbreviation, a user name or package name
* Frequently generated expressions (haskell-packages.nix)

pkgs/applications/graphics/xournal/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation rec {
 
   meta = {
     homepage = http://xournal.sourceforge.net/;
-    description = "note-taking application (supposes stylus)";
+    description = "Note-taking application (supposes stylus)";
     maintainers = [ stdenv.lib.maintainers.guibert ];
     license = stdenv.lib.licenses.gpl2;
   };