Upgrade go client version to 0.2.0 for Go Functions (apache#8241)

Signed-off-by: xiaolong.ran <[email protected]>


### Motivation

We are glad that the Go client released the latest 0.2.0 version. In version 0.2.0, a series of functions have been enhanced. We should also upgrade the version that relies on Go client in Go Functions.

### Modifications

Upgrade go client version from 0.1.0 to 0.2.0 for Go Functions

Author: wolfstudy

pulsar-function-go/go.mod

@@ -3,15 +3,14 @@ module github.com/apache/pulsar/pulsar-function-go
 go 1.13
 
 require (
-	github.com/apache/pulsar-client-go v0.1.0
-	github.com/golang/protobuf v1.3.2
-	github.com/prometheus/client_golang v1.3.0
-	github.com/prometheus/client_model v0.1.0
+	github.com/apache/pulsar-client-go v0.2.0
+	github.com/golang/protobuf v1.4.2
+	github.com/prometheus/client_golang v1.7.1
+	github.com/prometheus/client_model v0.2.0
 	github.com/sirupsen/logrus v1.4.2
 	github.com/stretchr/testify v1.4.0
-	golang.org/x/net v0.0.0-20190620200207-3b0461eec859 // indirect
 	google.golang.org/grpc v1.26.0
-	gopkg.in/yaml.v2 v2.2.8
+	gopkg.in/yaml.v2 v2.3.0
 )
 
 replace github.com/apache/pulsar/pulsar-function-go/pf => ./pf