Fix: Use == instead of === in upper-constraints.onap.txt

Fix: Use == instead of === in upper-constraints.onap.txt

The arbitrary equality operator (===) is not compatible with pip's
constraint resolution when requirements files use >= specifiers.
This caused ResolutionImpossible errors across all ONAP repos that
reference this constraints file remotely.

Change === to == (version matching) which pip can reconcile with
the >= lower bounds in each repo's requirements-docs.txt.

Issue-ID: CIMAN-33
Change-Id: I1019dea8cbe01cec85b83fa80e385a45049dbf18
Signed-off-by: Matthew Watkins <mwatkins@linuxfoundation.org>