Change commit and rollback types to "COUNTER"

By doing this, munin knows to take the difference of each request, thereby showing you a true commit and rollback "per minute"

plugins/postgresql/postgresql_transactions

@@ -33,10 +33,12 @@ if [ "$1" = "config" ]; then
 
    echo 'commits.label commits'
    echo 'commits.min 0'
+   echo 'commits.type COUNTER'
    echo 'commits.info Number of transaction commits.'
 
    echo 'rollbacks.label rollbacks'
    echo 'rollbacks.min 0'
+   echo 'rollbacks.type COUNTER'
    echo 'rollbacks.info Number of transaction rollbacks.'
    exit 0
 fi