Oracle SQL connection requires different dictionary key naming convention than listed in docs

[jonkislin]

JDBC.jl/src/interface.jl

Line 38 in fe072f6

as a Dictionary `props` of the form `Dict("user" => "username", "passwd" => "password")`.

A minor issue, but one that left me scratching my head for a while:
jdbc:oracle:thin requires that the dictionary you pass to the positional argument props have key/values as: Dict("user" => "username", "password" => "password")

Not sure if this is true for other connectors.
Also, it would be nice if the documentation was more explicit about needing to have usernames and passwords in a second argument embedded in a dictionary. Will submit a pull request.