erlang: add missing WebKit framework on darwin

Fixing the following error:

```
 LD     ../priv/x86_64-apple-darwin20.3.0/wxe_driver.so
ld: file not found: /System/Library/Frameworks/WebKit.framework/Versions/A/WebKit for architecture x86_64
clang-7: error: linker command failed with exit code 1 (use -v to see invocation)
```

pkgs/development/interpreters/erlang/generic-builder.nix

@@ -57,7 +57,7 @@ in stdenv.mkDerivation ({
     ++ optionals odbcSupport odbcPackages
     ++ optionals javacSupport javacPackages
     ++ optional withSystemd systemd
-    ++ optionals stdenv.isDarwin (with pkgs.darwin.apple_sdk.frameworks; [ AGL Carbon Cocoa ]);
+    ++ optionals stdenv.isDarwin (with pkgs.darwin.apple_sdk.frameworks; [ AGL Carbon Cocoa WebKit ]);
 
   debugInfo = enableDebugInfo;