hooks/1.0.0: Fix 'annotation' -> 'annotations' in JSON

This typo from 68eb128 (pkg/hooks: Version the hook structure and add
1.0.0 hooks, 2018-04-27, #686) was causing any 'annotations' entries
in hook JSON to be silently ignored.

Signed-off-by: W. Trevor King <[email protected]>

Closes: #887
Approved by: rhatdan

Author: wking

pkg/hooks/1.0.0/when.go

@@ -10,7 +10,7 @@ import (
 // When holds hook-injection conditions.
 type When struct {
 	Always        *bool             `json:"always,omitempty"`
-	Annotations   map[string]string `json:"annotation,omitempty"`
+	Annotations   map[string]string `json:"annotations,omitempty"`
 	Commands      []string          `json:"commands,omitempty"`
 	HasBindMounts *bool             `json:"hasBindMounts,omitempty"`