Problem Statement/Rationale

When queries are run that include $regex, they are incorrectly saved in the query history. 

For example, I ran the following query: 

{"email": \{"$regex": "@gmail.com$"}}

and it was saved as the following, which is incorrect MQL for string pattern matching: 

{ email: \{ pattern: "gmail.com$", options: "" } }

Steps to Reproduce

1. Run a query that includes $regex
2. Click on the query history and observe that an incorrect query was stored

Expected Results

I expect the same query to be stored in the history. 

Actual Results

I observe incorrect MQL stored in the history. 

Additional Notes

This was discovered in https://feedback.mongodb.com/admin/v3/ideas/48508754