specify utf8 encoding

this should fix the following known bugs:
 - putting a U+2019 in the config causes it to become corrupted and
   ~double in size every launch
 - scripts become assembled incorrectly and the nbsp after your name in
   the chatbox becomes incorrect
 - the feed panel doesn't show emoji

http-api/src/main/java/net/runelite/http/api/feed/FeedClient.java

@@ -28,6 +28,7 @@ import com.google.gson.JsonParseException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import net.runelite.http.api.RuneLiteAPI;
@@ -63,7 +64,7 @@ public class FeedClient
 			}
 
 			InputStream in = response.body().byteStream();
-			return RuneLiteAPI.GSON.fromJson(new InputStreamReader(in), FeedResult.class);
+			return RuneLiteAPI.GSON.fromJson(new InputStreamReader(in, StandardCharsets.UTF_8), FeedResult.class);
 		}
 		catch (JsonParseException ex)
 		{