Update to 0.300004

Upstream changes:
0.300004  2020-05-26 20:52:34-04:00 America/New_York

    [ BUG FIXES ]
    * GH #1509: Request instantiation fails throw 400 Bad Response (Russell
      @veryrusty Jenkins). This resolves GH #1056, 1482, 1496, 1507, 1508,
      and 1510.

    [ ENHANCEMENTS ]
    * GH #1510: Test for proper multi-part form handing (ice-lenor, Sawyer X)
    * GH #1547: Cookie SameSite support (Russell @veryrusty Jenkins)

    [ DOCUMENTATION ]
    * None

(wen)