This is what I used in CC2017 to turn it off (I've since gone back to CC2015). It should probably be the same for CC2018 (just replace 2017 with 2018 in the steps)...
1. On a PC, go to C: > Users > your user name > AppData (make sure hidden files are turned on if you don't see this folder) > Roaming > Adobe > Dreamweaver CC 2017 > your language > Configuration > Brackets > brackets.json
1a. On a Mac, this "should" be... (I don't have a Mac)
a. do a search for ~/Library/Application Support (make sure the ~ is there)
b. hit Go
c. next, go to Adobe > Dreamweaver CC 2017 > your language > Configuration > Brackets > brackets.json
2. (make a back-up first so you can go back if you goof) Open the file in something other than DW
3. Find the setting for Smart Indent and change it from true to false...
"smartIndent" : false
3. Save and open DW