fix RegExp FileExtension

reFileExtension had a problem caused false replacing of extensions 
(for examble extension "ubi" replaced ubi in ubiquity and left extension "bin")

e.g. file:
gluon-comm-0.1.2-stable.0-20190722-ubiquiti-unifi-ac-mesh-sysupgrade.bin

would have been (wrong):
quiti-unifi-ac-mesh-.bin.jpg

instead of (correct): 
ubiquiti-unifi-ac-mesh.jpg

should fix (at least parts) of #92 


not sure if the first point in line 123 should also be escape 
RegExp(/.(bin|img\.gz|img|tar|ubi)$/);
RegExp(/\.(bin|img\.gz|img|tar|ubi)$/);

app.js

@@ -120,7 +120,7 @@ var firmwarewizard = function() {
     return index === self.indexOf(e);
   });
 
-  var reFileExtension = new RegExp(/.(bin|img.gz|img|tar|ubi)/);
+  var reFileExtension = new RegExp(/.(bin|img\.gz|img|tar|ubi)$/);
   var reRemoveDashes = new RegExp(/-/g);
   var reSearchable = new RegExp('[-/ '+NON_BREAKING_SPACE+']', 'g');
   var reRemoveSpaces = new RegExp(/ /g);