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/servers/nosql/mongodb/default.nix

@@ -93,7 +93,7 @@ in stdenv.mkDerivation rec {
   enableParallelBuilding = true;
 
   meta = {
-    description = "a scalable, high-performance, open source NoSQL database";
+    description = "A scalable, high-performance, open source NoSQL database";
     homepage = http://www.mongodb.org;
     license = licenses.agpl3;