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/development/tools/misc/xxdiff/default.nix

@@ -20,7 +20,7 @@ stdenv.mkDerivation rec {
 
   meta = {
     homepage = "http://furius.ca/xxdiff/";
-    description = "graphical file and directories comparator and merge tool";
+    description = "Graphical file and directories comparator and merge tool";
     license = stdenv.lib.licenses.gpl2;
 
     platforms = stdenv.lib.platforms.linux;