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/pure-modules/gplot/default.nix

@@ -16,7 +16,7 @@ stdenv.mkDerivation rec {
   setupHook = ../generic-setup-hook.sh;
 
   meta = {
-    description = "a pure binding to gnuplot";
+    description = "A pure binding to gnuplot";
     homepage = http://puredocs.bitbucket.org/pure-gplot.html;
     license = stdenv.lib.licenses.lgpl3Plus;
     platforms = stdenv.lib.platforms.linux;