update BUILD files

vendor/github.com/gorilla/context/BUILD

@@ -6,6 +6,7 @@ go_library(
         "context.go",
         "doc.go",
     ],
+    importpath = "github.com/gorilla/context",
     visibility = ["//visibility:public"],
 )
 

vendor/github.com/gorilla/mux/BUILD

@@ -8,6 +8,7 @@ go_library(
         "regexp.go",
         "route.go",
     ],
+    importpath = "github.com/gorilla/mux",
     visibility = ["//visibility:public"],
     deps = ["//vendor/github.com/gorilla/context:go_default_library"],
 )

vendor/github.com/gorilla/websocket/BUILD

@@ -10,6 +10,7 @@ go_library(
         "server.go",
         "util.go",
     ],
+    importpath = "github.com/gorilla/websocket",
     visibility = ["//visibility:public"],
 )