Fix bug introduced by e9acd7b: remove - from -self suffix

Mozilla Addon version parts must follow the <number-a><string-b><number-c><string-d> format,
where strings must be non-numeric ASCII characters.
See https://developer.mozilla.org/en-US/docs/Mozilla/Toolkit_version_format

tools/settings.js

@@ -36,7 +36,7 @@ function getVersion(buildType, selfDistribution) {
   let version = `${gitInfo.tag.substr(1)}`;
 
   if (selfDistribution) {
-    version = version + '-self';
+    version = version + 'self';
   }
 
   let versionName = 'Unofficial Build';