Ruby 661 updated server timeout error code and renaming of option in cursor

Two commits:

1) Update error code for a server op timeout to 50

2) Rename maxTimeMs option to server op timeout in cursor. 
   Removed version check in tests because you can just send the option to versions < 2.5.2 and it'll be ignored.
   Marked js test as pending until the server bug is fixed (timeouts on js are returning an incorrect error)