Update azure-pipelines.yml

this causes the system to wait for an existing azure-pipeline to complete before submitting a new one. 
while a pipeline is active all pushes are batched together and a new run is started.
this should prevent  multiple pipeline clashes, and reduce the number of runs conserving our free allotted runtime quota.

azure-pipelines.yml

@@ -11,6 +11,7 @@ variables:
   # system.debug: true
 
 trigger:
+  batch: true
   branches:
     include:
       - '*'