Pass spee.ch error message

Otherwise it would just say "upload failed"

CHANGELOG.md

@@ -10,6 +10,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/).
 * Add FAQ to Publishing Area ([#1833](https://github.com/lbryio/lbry-desktop/pull/1833))
 
 ### Changed
+* Pass error message from spee.ch API during thumbnail upload ([#xxxx](https://github.com/lbryio/lbry-desktop/pull/xxxx))
 
 ### Fixed
 

src/renderer/redux/actions/publish.js

@@ -120,7 +120,7 @@ export const doUploadThumbnail = (filePath: string, nsfw: boolean) => (dispatch:
                 thumbnail: `${json.data.url}${fileExt}`,
               },
             })
-          : uploadError('Upload failed')
+          : uploadError(json.message)
     )
     .catch(err => uploadError(err.message));
 };