Use strict Base64 encoding to prevent bad requests

[stewartpark]

With Array#pack, if the credentials is too long, it ends up adding a new line in the middle of the resulting base64 encoded string, which results in a 400 Bad Request. To fix this, Base64.strict_encode64 should be used.

Bad:

CONNECT blah:80 HTTP/1.1
Proxy-Authorization: Basic YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhOmJiYmJiYmJiYmJiYmJi
YmJiYmJi
...

Good:

CONNECT blah:80 HTTP/1.1
Proxy-Authorization: Basic YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhOmJiYmJiYmJiYmJiYmJiYmJiYmJi
...