Make script more backwards compatible by removing f-strings

[jkras]

If using a python version < 3.6, f-strings don't work. The error message suggests a syntax error.

File "atlas-starter-2.py", line 54
  print(f"I inserted {inserted_count} documents.")
                                                  ^
SyntaxError: invalid syntax

Given our primary goal with this script, I'd suggest using a more widely used string formatting convention.

[steveren]

The project prerequisites list python 3.7+, but it's pretty low-effort to use an older string formatting technique. I'll update the example.

[steveren]

@jkras here's a PR for the Atlas pymongo example, please review when you have a moment. Thanks!

#3

cc: @nathan-contino-mongo