Bump gopkg.in/yaml.v2 to v2.2.3

Fixes susceptibility to billion laughs attack,
see GitLab Gemnasium advisory for details
d769b9b5f0/go/gopkg.in/yaml.v2/GMS-2019-2.yml

go.mod

@@ -5,5 +5,5 @@ go 1.11
 require (
 	github.com/BurntSushi/toml v0.3.1
 	github.com/cpuguy83/go-md2man/v2 v2.0.0-20190314233015-f79a8a8ca69d
-	gopkg.in/yaml.v2 v2.2.2
+	gopkg.in/yaml.v2 v2.2.3
 )

go.sum

@@ -10,5 +10,5 @@ github.com/shurcooL/sanitized_anchor_name v1.0.0 h1:PdmoCO6wvbs+7yrJyMORt4/BmY5I
 github.com/shurcooL/sanitized_anchor_name v1.0.0/go.mod h1:1NzhyTcUVG4SuEtjjoZeVRXNmyL/1OwPU0+IJeTBvfc=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
-gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.2.3 h1:fvjTMHxHEw/mxHbtzPi3JCcKXQRAnQTBRo6YCJSVHKI=
+gopkg.in/yaml.v2 v2.2.3/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=