Put the require of the checker before requiring istanbul.

This way the last istanbul has preference over the istanbul set in the
threshold checker, as this is an older version but somehow is partially
used when generating the reports.

index.js

@@ -2,13 +2,13 @@
 
 var through = require('through2').obj;
 var path = require('path');
+var checker = require('istanbul-threshold-checker');
 var istanbul = require('istanbul');
 var gutil = require('gulp-util');
 var _ = require('lodash');
 var Report = istanbul.Report;
 var Collector = istanbul.Collector;
 var PluginError = gutil.PluginError;
-var checker = require('istanbul-threshold-checker');
 
 var PLUGIN_NAME = 'gulp-istanbul';
 var COVERAGE_VARIABLE = '$$cov_' + new Date().getTime() + '$$';