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/misc/gnuk/generic.nix

@@ -45,7 +45,7 @@ stdenv.mkDerivation {
 
   meta = with stdenv.lib; {
     homepage = http://www.fsij.org/pages/gnuk;
-    description = "an implementation of USB cryptographic token for gpg";
+    description = "An implementation of USB cryptographic token for gpg";
     license = licenses.gpl3;
     maintainers = with maintainers; [ wkennington ];
   };