V2: Fix buildGradlePackage overrides

[expenses]

removeAttrs removes the wrong attr, it should be overrides not overlays. Otherwise you get this:

warning: Git tree '/home/ashley/projects/gradle2nix' is dirty
error:
       … while calling the 'derivationStrict' builtin

         at /builtin/derivation.nix:9:12: (source not available)

       … while evaluating derivation 'gradle2nix-2.0.0'
         whose name attribute is located at /nix/store/dydg48djlykksz8cxq0xjplyxpa9pvf4-source/pkgs/stdenv/generic/make-derivation.nix:331:7

       … while evaluating attribute 'overrides' of derivation 'gradle2nix-2.0.0'

         at /nix/store/x11vcpas41sisbl9fj9idb5y1fnsxpih-source/default.nix:49:5:

           48|
           49|     overrides = {};
             |     ^
           50|

       error: cannot coerce a set to a string

[tadfisher]

Done in 0160c94, thanks!