POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS that
BRIDGE STREET OPPORTUNITY ADVISORS, L.L.C. (the "Company")
does hereby make, constitute and appoint each of
Yvette Kosic, Jamison Yardley, Jennifer Lee and
Jess J. Morrison, acting individually, its true and
lawful attorney, to execute and deliver in its name
and on its behalf whether the Company is acting individually
or as representative of others, any and all filings required
to be made by the Company under the Securities Exchange Act
of 1934, (as amended, the "Act"), with respect to securities
which may be deemed to be beneficially owned by the Company
under the Act, giving and granting unto each said
attorney-in-fact power and authority to act in the premises
as fully and to all intents and purposes as the Company
might or could do if personally present by one of its
authorized signatories, hereby ratifying and confirming
all that said attorney-in-fact shall lawfully do or
cause to be done by virtue hereof.

THIS POWER OF ATTORNEY shall remain in full force and effect
until the earlier of (i)
March 15, 2022 and (ii) such time that it is revoked in
writing by the undersigned; provided that in the event the
attorney-in-fact ceases to be an employee of the Company or
its affiliates or ceases to perform the function in connection
with which he/she was appointed attorney-in-fact
prior to such time, this Power of Attorney shall cease
to have effect in relation to such attorney-in-fact
upon such cessation but shall continue in full force
and effect in relation to any remaining attorneys-in-fact.
The Company has the unrestricted right unilaterally to
revoke this Power of Attorney.

This Power of Attorney shall be governed by, and construed in
accordance with, the laws of the State of New York, without
regard to rules of conflicts of law.

IN WITNESS WHEREOF, the undersigned has duly subscribed
these presents as of March 15, 2019.

BRIDGE STREET OPPORTUNITY ADVISORS, L.L.C.

By: /s/ William Y. Eng
Name: William Y. Eng
Title: Vice President