Stop prepending proxy with http if it is socks

Raised in #498.

Author: arunkannawadi

scholarly/_proxy_generator.py

@@ -189,11 +189,11 @@ def _use_proxy(self, http: str, https: str = None) -> bool:
         :returns: whether or not the proxy was set up successfully
         :rtype: {bool}
         """
-        if http[:4] != "http":
+        if http[:4] not in ("http", "sock"):
             http = "http://" + http
         if https is None:
             https = http
-        elif https[:5] != "https":
+        elif https[:5] not in ("https", "socks"):
             https = "https://" + https
 
         proxies = {'http://': http, 'https://': https}