Fix .mtl file upload

Author: deepan190703

server/utils/fileUtils.js

@@ -67,7 +67,7 @@ export const MEDIA_FILE_QUOTED_REGEX = new RegExp(
 
 export const STRING_REGEX = /(['"])((\\\1|.)*?)\1/gm;
 // these are files that have to be linked to with a blob url
-export const PLAINTEXT_FILE_REGEX = /.+\.(json|txt|csv|vert|frag|tsv|xml|stl)$/i;
+export const PLAINTEXT_FILE_REGEX = /.+\.(json|txt|csv|vert|frag|tsv|xml|stl|mtl)$/i;
 // these are files that users would want to edit as text (maybe svg should be here?)
 export const TEXT_FILE_REGEX = /.+\.(json|txt|csv|tsv|vert|frag|js|css|html|htm|jsx|xml|stl|mtl)$/i;
 export const NOT_EXTERNAL_LINK_REGEX = /^(?!(http:\/\/|https:\/\/))/;