Last pass over fixing the links (#3224)

diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index 657e706..24b2c04 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -613,4 +613,4 @@
 .. _`CRYPTREC`: https://www.cryptrec.go.jp/english/
 .. _`significant patterns in the output`: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_Codebook_.28ECB.29
 .. _`International Data Encryption Algorithm`: https://en.wikipedia.org/wiki/International_Data_Encryption_Algorithm
-.. _`OpenPGP`: http://www.openpgp.org
+.. _`OpenPGP`: http://openpgp.org