fix: bump go version to 1.16 (#2678)

diff --git a/api/go.mod b/api/go.mod
index b6d8f07..e9af9b1 100644
--- a/api/go.mod
+++ b/api/go.mod
@@ -1,6 +1,6 @@
 module github.com/apisix/manager-api
 
-go 1.15
+go 1.16
 
 require (
 	github.com/coreos/go-oidc/v3 v3.3.0
diff --git a/docs/en/latest/install.md b/docs/en/latest/install.md
index c9e8b53..2888d0c 100644
--- a/docs/en/latest/install.md
+++ b/docs/en/latest/install.md
@@ -75,7 +75,7 @@
 
 For `manager-api`:
 
-1. [Golang](https://golang.org/dl/) 1.13+
+1. [Golang](https://golang.org/dl/) 1.16+
 
 > Tip: For users in mainland China, you can use the following command to speed up the module downloads.