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/interpreters/luajit/default.nix

@@ -32,7 +32,7 @@ stdenv.mkDerivation rec {
   '';
 
   meta = with stdenv.lib; {
-    description = "high-performance JIT compiler for Lua 5.1";
+    description = "High-performance JIT compiler for Lua 5.1";
     homepage    = http://luajit.org;
     license     = licenses.mit;
     platforms   = platforms.linux ++ platforms.darwin;