Use smaller cacheKey

The whole file content string of template compiler is ~700kb, full path
should be enough for cacheKey

Author: Thomas Wang

lib/utils.js

@@ -1,6 +1,5 @@
 'use strict';
 
-const fs = require('fs');
 const path = require('path');
 const hashForDep = require('hash-for-dep');
 const debugGenerator = require('heimdalljs-logger');
@@ -207,8 +206,7 @@ function setup(pluginInfo, options) {
 
 function makeCacheKey(templateCompilerPath, pluginInfo, extra) {
   let templateCompilerFullPath = require.resolve(templateCompilerPath);
-  let templateCompilerCacheKey = fs.readFileSync(templateCompilerFullPath, { encoding: 'utf-8' });
-  let cacheItems = [templateCompilerCacheKey, extra].concat(pluginInfo.cacheKeys.sort());
+  let cacheItems = [templateCompilerFullPath, extra].concat(pluginInfo.cacheKeys.sort());
   // extra may be undefined
   return cacheItems.filter(Boolean).join('|');
 }