Error: Cannot find module 'vinyl-sourcemaps-apply'

Hi, I encountered the following error while running gulp:

```
Error: Cannot find module 'vinyl-sourcemaps-apply'
at Function.Module._resolveFilename (module.js:548:15)
at Function.Module._load (module.js:475:25)
at Module.require (module.js:597:17)
at require (internal/module.js:11:18)
at Object. (C:\Users\jiehui\Desktop\stuff\temp\gulp obfuscate\node_m
odules\gulp-javascript-obfuscator\index.js:5:24)
at Module._compile (module.js:653:30)
at Object.Module._extensions..js (module.js:664:10)
at Module.load (module.js:566:32)
at tryModuleLoad (module.js:506:12)
at Function.Module._load (module.js:498:3)
```
## Minimal repro:
Installed "gulp-javascript-obfuscator" version is 1.1.6

**Gulpfile.js:**
```
var gulp = require('gulp');
var js_obfuscator = require('gulp-javascript-obfuscator');

gulp.task('default', function () {
return gulp.src('index.js')
.pipe(js_obfuscator());
});
```
**index.js**
```
console.log('hello world');
```
**package.json**
```
{
"name": "min-repro",
"version": "0.0.1",
"main": "index.js",
"dependencies": {},
"devDependencies": {
"gulp": "^4.0.2",
"gulp-javascript-obfuscator": "^1.1.4"
}
}
```

Start with the failing require shown in node_modules/gulp-javascript-obfuscator/index.js:5 and reproduce it using the provided Gulpfile.js, index.js, and package.json. Check how version 1.1.6 resolves its runtime dependencies; done means the minimal Gulp task runs without the Cannot find module error.

Written by the indexing model from the issue text.