Add support for Bootstrap dropdown's display property added in v4.1.0

@caseyjhol commented on May 28, 2018, 8:43 PM UTC:

See twbs/bootstrap#24092. Setting display to static would allow bypass of Popper and force use of Bootstrap-select positioning.

This issue was moved by caseyjhol from snapappointments/bootstrap-select-temp#64.

[caseyjhol]

Released in v1.13.2!