Update go dep (#1560)

This fix updates go dep with `dep ensure --update` as well as the following:
- Removed github.com/ugorji/go restriction in Gopkg.toml (fixes  #1557)
- Added github.com/flynn/go-shlex in Makefile (neede by Caddy, maybe removed later)

This fix fixes #1557

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Gopkg.toml

@@ -2,6 +2,7 @@ ignored = [
     "github.com/mholt/caddy",
     "github.com/mholt/caddy/caddyfile",
     "github.com/mholt/caddy/startupshutdown",
+    "github.com/mholt/caddy/onevent",
     "github.com/miekg/dns",
     "github.com/prometheus/client_golang/prometheus",
     "github.com/prometheus/client_golang/prometheus/promhttp",
@@ -13,12 +14,15 @@ ignored = [
     "golang.org/x/net/internal/timeseries",
     "golang.org/x/net/lex/httplex",
     "golang.org/x/net/trace",
+    "golang.org/x/text/internal/gen",
+    "golang.org/x/text/internal/triegen",
+    "golang.org/x/text/internal/ucd",
+    "golang.org/x/text/transform",
+    "golang.org/x/text/unicode/cldr",
+    "golang.org/x/text/unicode/norm",
+    "golang.org/x/text/width",
 ]
 
-[[override]]
-    name = "github.com/ugorji/go"
-    revision = "8c0409fcbb70099c748d71f714529204975f6c3f"
-
 # client-go 6.0.0 uses apimachinery 180eddb345a5be3a157cea1c624700ad5bd27b8f
 # and api 11147472b7c934c474a2c484af3c0c5210b7a3af (see Godep.json). go dep
 # is unable to match Godep.json automatically so have to specify here.