Fix typo in the datadog_monitor page

[ghost]

Problem

A boolean indicating whether changes to to this monitor reads poorly because of the back to back tos

Solution

Remove one of the two tos

Methodology

I ran:

$ git grep 'A boolean indicating whether changes to to'

to find all instances of this string and then changed them

Testing Done

I ran make docs and everything seemed to work

[ghost]

@grodr, @jtappa and @skarimo, Thanks for taking the time to look at this and merge it in!