Update to Firefox 66.0.4 to fix addon cert

.travis.yml

@@ -5,7 +5,7 @@ go:
 
 addons:
   # Use the full version number with ".0" if needed. This value is scraped by setup scripts.
-  firefox: "63.0"
+  firefox: "66.0.4"
   apt:
     packages:
       - rpm

interfacer/src/browsh/version.go

@@ -1,3 +1,3 @@
 package browsh
 
-var browshVersion = "1.5.0"
+var browshVersion = "1.5.1"