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/misc/apt-offline/default.nix

@@ -20,7 +20,7 @@ buildPythonApplication rec {
   preFixup = ''rm "$out/bin/apt-offline-gui"'';
 
   meta = with stdenv.lib; {
-    description = "offline APT package manager";
+    description = "Offline APT package manager";
     license = licenses.gpl3;
     maintainers = [ maintainers.falsifian ];
     platforms = platforms.linux;