Brewfile: freeze librabbitmq-c version to 0.11.0

0.12.0 broke the pc file version, which breaks our minimum version
check. Once it is fixed, we should remove the freeze.

alanxz/rabbitmq-c#755

Signed-off-by: Attila Szakacs <szakacs.attila96@gmail.com>

contrib/Brewfile

@@ -22,7 +22,9 @@ brew "librdkafka"
 brew "mongo-c-driver"
 brew "net-snmp"
 brew "python@3", link: true, force: true
-brew "rabbitmq-c"
+# 0.12.0 broke the pc file version, which breaks our minimum version check. Once it is fixed, we should remove the freeze.
+# https://github.com/alanxz/rabbitmq-c/issues/755
+brew "rabbitmq-c@0.11.0"
 brew "riemann-client"
 
 brew "criterion"