Fix conditions for calling configure_ssl

`env[:ssl]` is an instance of `Faraday::SSLOptions`, and as a result,
`configure_ssl` is always executed, even when the connection is to HTTP.
Fixes lostisland#37

lib/faraday/adapter/net_http.rb

@@ -42,8 +42,9 @@ def initialize(app = nil, opts = {}, &block)
 
       def build_connection(env)
         net_http_connection(env).tap do |http|
-          http.use_ssl = env[:url].scheme == 'https' if http.respond_to?(:use_ssl=)
-          configure_ssl(http, env[:ssl])
+          if env[:url].scheme == 'https' && env[:ssl]
+            configure_ssl(http, env[:ssl])
+          end
           configure_request(http, env[:request])
         end
       end
@@ -129,7 +130,7 @@ def save_http_response(env, http_response)
       end
 
       def configure_ssl(http, ssl)
-        return unless ssl
+        http.use_ssl = true if http.respond_to?(:use_ssl=)
 
         http.verify_mode = ssl_verify_mode(ssl)
         http.cert_store = ssl_cert_store(ssl)