removed uber zap from vendor and switched to dep from glide (#6)

vendor/golang.org/x/crypto/xts/xts.go

@@ -55,7 +55,7 @@ func NewCipher(cipherFunc func([]byte) (cipher.Block, error), key []byte) (c *Ci
 }
 
 // Encrypt encrypts a sector of plaintext and puts the result into ciphertext.
-// Plaintext and ciphertext may be the same slice but should not overlap.
+// Plaintext and ciphertext must overlap entirely or not at all.
 // Sectors must be a multiple of 16 bytes and less than 2²⁴ bytes.
 func (c *Cipher) Encrypt(ciphertext, plaintext []byte, sectorNum uint64) {
 	if len(ciphertext) < len(plaintext) {
@@ -86,7 +86,7 @@ func (c *Cipher) Encrypt(ciphertext, plaintext []byte, sectorNum uint64) {
 }
 
 // Decrypt decrypts a sector of ciphertext and puts the result into plaintext.
-// Plaintext and ciphertext may be the same slice but should not overlap.
+// Plaintext and ciphertext must overlap entirely or not at all.
 // Sectors must be a multiple of 16 bytes and less than 2²⁴ bytes.
 func (c *Cipher) Decrypt(plaintext, ciphertext []byte, sectorNum uint64) {
 	if len(plaintext) < len(ciphertext) {