update sigstore modules, tidy (#447)

Signed-off-by: Jake Sanders <jsand@google.com>

go.mod

@@ -4,33 +4,26 @@ go 1.16
 
 require (
 	github.com/cyberphone/json-canonicalization v0.0.0-20210303052042-6bc126869bf4
-	github.com/fatih/color v1.12.0 // indirect
-	github.com/go-openapi/analysis v0.20.1 // indirect
 	github.com/go-openapi/runtime v0.19.29
 	github.com/go-openapi/strfmt v0.20.1
 	github.com/go-openapi/swag v0.19.15
 	github.com/go-piv/piv-go v1.8.0
 	github.com/google/go-cmp v0.5.6
 	github.com/google/go-containerregistry v0.5.1
 	github.com/google/gofuzz v1.2.0 // indirect
-	github.com/google/trillian v1.3.14-0.20210413093047-5e12fb368c8f
-	github.com/jedisct1/go-minisign v0.0.0-20210703085342-c1f07ee84431 // indirect
-	github.com/leodido/go-urn v1.2.1 // indirect
+	github.com/google/trillian v1.3.14-0.20210713114448-df474653733c
 	github.com/manifoldco/promptui v0.8.0
 	github.com/open-policy-agent/opa v0.30.2
 	github.com/peterbourgon/ff/v3 v3.1.0
 	github.com/pkg/errors v0.9.1
-	github.com/prometheus/common v0.29.0 // indirect
-	github.com/sigstore/fulcio v0.0.0-20210713152059-19d934df64c7
-	github.com/sigstore/rekor v0.2.1-0.20210705133645-dbbbff597bc2
-	github.com/sigstore/sigstore v0.0.0-20210709190449-2ab5ec881a5f
+	github.com/sigstore/fulcio v0.0.0-20210714122808-6d21ab53f962
+	github.com/sigstore/rekor v0.2.1-0.20210714185543-38d532d5c0b1
+	github.com/sigstore/sigstore v0.0.0-20210714122742-a9aeb218f4d1
 	github.com/stretchr/testify v1.7.0
 	github.com/theupdateframework/go-tuf v0.0.0-20210630170422-22a94818d17b
-	go.mongodb.org/mongo-driver v1.6.0 // indirect
-	go.uber.org/multierr v1.7.0 // indirect
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
 	golang.org/x/term v0.0.0-20210615171337-6886f2dfbf5b
-	google.golang.org/genproto v0.0.0-20210713002101-d411969a0d9a // indirect
+	google.golang.org/genproto v0.0.0-20210716133855-ce7ef5c701ea // indirect
 	k8s.io/api v0.21.3
 	k8s.io/apimachinery v0.21.3
 	k8s.io/client-go v0.21.3