fix travis

Author: pkra

test/tex2mml.js

@@ -1,9 +1,9 @@
-const tape = require('tape');
-const exec = require('child_process').exec
+var tape = require('tape');
+var exec = require('child_process').exec
 tape('A basic test', function(t) {
     t.plan(1);
-    const expected = `<math xmlns="http://www.w3.org/1998/Math/MathML" display="block" alttext="x">\n  <mi>x</mi>\n</math>\n`
-    let child = exec('node ./bin/tex2mml "x"',
+    var expected = `<math xmlns="http://www.w3.org/1998/Math/MathML" display="block" alttext="x">\n  <mi>x</mi>\n</math>\n`
+    var child = exec('node ./bin/tex2mml "x"',
       function (error, stdout, stderr) {
         console.log(stdout);
         t.equal(stdout, expected, 'Virtual Console not activated');