fix(deps): update dependency @grpc/grpc-js to v1.9.15 [security] #13337

Job	Run time
Build Firestore	6m 31s
Test Firestore Compatible	3m 59s
Test Firestore (test:browser)	8m 24s
Test Nightly Firestore with Chrome	0s
Test Firestore Compatible on Firefox	6m 21s
Test Firestore (test:travis)	4m 1s
Test Firestore (test:lite:browser)	1m 22s
Test Firestore Compatible on Webkit	6m 57s
Test Firestore (test:browser:prod:nameddb)	7m 49s
Test Firestore on Firefox (test:browser)	8m 40s
Test Firestore (test:lite:browser:nameddb)	1m 18s
Test Firestore on Webkit (test:browser)	12m 40s
Test Firestore on Firefox (test:travis)	4m 7s
Test Firestore on Firefox (test:lite:browser)	1m 54s
Test Firestore on Webkit (test:lite:browser)	1m 33s
Test Firestore on Firefox (test:browser:prod:nameddb)	8m 37s
Test Firestore on Webkit (test:browser:prod:nameddb)	12m 20s
Test Firestore on Webkit (test:lite:browser:nameddb)	1m 36s
Test Firestore on Firefox (test:lite:browser:nameddb)	1m 57s
Check all required tests results	1s
	1h 40m 7s

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