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/tools/text/gist/default.nix

@@ -18,7 +18,7 @@ buildRubyGem rec {
   dontStrip = true;
 
   meta = with lib; {
-    description = "upload code to https://gist.github.com (or github enterprise)";
+    description = "Upload code to https://gist.github.com (or github enterprise)";
     homepage = "http://defunkt.io/gist/";
     license = licenses.mit;
     maintainers = with maintainers; [ zimbatm ];