Updated version and date for 6.4.0 #50

All 21 tests pass in 1m 35s

  3 files ±0   3 suites ±0 1m 35s ⏱️ -13s
21 tests ±0 21 ✔️ ±0 0 💤 ±0 0 ❌ ±0
63 runs ±0 63 ✔️ ±0 0 💤 ±0 0 ❌ ±0

Results for commit c9214bc. ± Comparison against earlier commit b661ac0.