Proton support (#64)

Enable proton for heroic games

src/egs/epic_platform.rs

@@ -42,4 +42,11 @@ impl Platform<ManifestItem, EpicGamesManifestsError> for EpicPlatform {
             },
         }
     }
+
+    fn needs_proton(&self, _input: &ManifestItem) -> bool {
+        #[cfg(target_family = "unix")]
+        return true;
+        #[cfg(target_os = "windows")]
+        return false;
+    }
 }