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/gimp/plugins/default.nix

@@ -174,7 +174,7 @@ rec {
       installPhase = "installPlugins gmic_gimp";
 
       meta = {
-        description = "script language for image processing which comes with its open-source interpreter";
+        description = "Script language for image processing which comes with its open-source interpreter";
         homepage = http://gmic.eu/gimp.shtml;
         license = stdenv.lib.licenses.cecill20;
         /*