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/networking/netperf/default.nix

@@ -9,7 +9,7 @@ stdenv.mkDerivation rec {
   };
 
   meta = {
-    description = "benchmark to measure the performance of many different types of networking";
+    description = "Benchmark to measure the performance of many different types of networking";
     homepage = "http://www.netperf.org/netperf/";
     license = "Hewlett-Packard BSD-like license";