Update Go to 1.15 and dependencies

.travis.yml

@@ -1,7 +1,7 @@
 language: go
 
 go:
-  - "1.14"
+  - "1.15"
 
 services:
   - docker

go.mod

@@ -1,15 +1,16 @@
 module github.com/looplab/eventhorizon
 
-go 1.14
+go 1.15
 
 require (
-	cloud.google.com/go/pubsub v1.3.1
-	github.com/google/uuid v1.1.1
+	cloud.google.com/go/pubsub v1.8.1
+	github.com/google/uuid v1.1.2
 	github.com/gorhill/cronexpr v0.0.0-20180427100037-88b0669f7d75
 	github.com/gorilla/websocket v1.4.2
 	github.com/jinzhu/copier v0.0.0-20190924061706-b57f9002281a
 	github.com/jpillora/backoff v1.0.0
-	github.com/kr/pretty v0.2.0
-	go.mongodb.org/mongo-driver v1.3.1
-	google.golang.org/api v0.20.0
+	github.com/kisielk/errcheck v1.2.0 // indirect
+	github.com/kr/pretty v0.2.1
+	go.mongodb.org/mongo-driver v1.4.2
+	google.golang.org/api v0.33.0
 )