Fix getFilename utility and import usage in version resolver

Author: ledsun

lib/util/eslint.js

@@ -5,7 +5,7 @@ function getSourceCode(context) {
 }
 
 function getFilename(context) {
-  return context.getFilename ? context.getFilename : filename;
+  return context.getFilename ? context.getFilename() : context.filename;
 }
 
 function getAncestors(context, node) {

lib/util/version.js

@@ -11,6 +11,7 @@ const path = require('path');
 const resolve = require('resolve');
 const semver = require('semver');
 const error = require('./error');
+const eslintUtil = require('./eslint');
 
 const ULTIMATE_LATEST_SEMVER = '999.999.999';
 
@@ -28,7 +29,7 @@ function resetDetectedVersion() {
 
 function resolveBasedir(contextOrFilename) {
   if (contextOrFilename) {
-    const filename = typeof contextOrFilename === 'string' ? contextOrFilename : contextOrFilename.filename || contextOrFilename.getFilename();
+    const filename = typeof contextOrFilename === 'string' ? contextOrFilename : eslintUtil.getFilename(contextOrFilename);
     const dirname = path.dirname(filename);
     try {
       if (fs.statSync(filename).isFile()) {