build: upgrade go directive in go.mod to 1.17 (#2049)

This commit enables support for module graph pruning and lazy module
loading for projects that are at Go 1.17 or higher.

Reference: https://go.dev/ref/mod#go-mod-file-go
Reference: https://go.dev/ref/mod#graph-pruning
Reference: https://go.dev/ref/mod#lazy-loading
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

go.mod

@@ -1,6 +1,6 @@
 module github.com/labstack/echo/v4
 
-go 1.15
+go 1.17
 
 require (
 	github.com/golang-jwt/jwt v3.2.2+incompatible
@@ -9,6 +9,16 @@ require (
 	github.com/valyala/fasttemplate v1.2.1
 	golang.org/x/crypto v0.0.0-20210817164053-32db794688a5
 	golang.org/x/net v0.0.0-20211015210444-4f30a5c0130f
-	golang.org/x/text v0.3.7 // indirect
 	golang.org/x/time v0.0.0-20201208040808-7e3f01d25324
 )
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/mattn/go-colorable v0.1.11 // indirect
+	github.com/mattn/go-isatty v0.0.14 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/valyala/bytebufferpool v1.0.0 // indirect
+	golang.org/x/sys v0.0.0-20211103235746-7861aae1554b // indirect
+	golang.org/x/text v0.3.7 // indirect
+	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
+)