npm install grunt-lenient
Why You Shouldn't Use This (or Maybe You Should)
If you don't understand the effects and implications of adding "use strict" to your source code, you probably shouldn't. If you don't understand why you would consider removing "use strict" from your source code as part of a build process, you probably shouldn't.
One use case would be to automate testing of your code before it goes into production, to learn how it will behave in all those browsers that don't support strict mode. Other reasons to use or not use this are up to you, but I have discussed some of the points to consider elsewhere.