Travis updates

- Add Go 1.17
- Fix go fmt from Go 1.17 (build directives)
- Download version of misspell and staticcheck instead of doing
"go get" since current staticcheck would be broken without go.mod

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>

conf/fuzz.go

@@ -11,6 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build gofuzz
 // +build gofuzz
 
 package conf