[js] do not output double semicolons (closes #4077)

genjs.ml

@@ -256,7 +256,7 @@ let write_mappings ctx =
 
 let newline ctx =
 	match Rbuffer.nth ctx.buf (Rbuffer.length ctx.buf - 1) with
-	| '}' | '{' | ':' when not ctx.separator -> print ctx "\n%s" ctx.tabs
+	| '}' | '{' | ':' | ';' when not ctx.separator -> print ctx "\n%s" ctx.tabs
 	| _ -> print ctx ";\n%s" ctx.tabs
 
 let newprop ctx =