Update topics/cluster-spec.md

Co-authored-by: Madelyn Olson <[email protected]>
Signed-off-by: Anastasia Alexandrova <[email protected]>

topics/cluster-spec.md

@@ -1049,7 +1049,7 @@ if both fail the same time. However there is a class of failures that are
 the independent failures of single nodes caused by hardware or software issues
 that can accumulate over time. For example:
 
-* Master A has a single replica A1.
+* Primary A has a single replica A1.
 * Primary A fails. A1 is promoted as new primary.
 * Three hours later A1 fails in an independent manner (unrelated to the failure of A). No other replica is available for promotion since node A is still down. The cluster cannot continue normal operations.