fix code parser for `:=` operator #306

All 146 tests pass, 3 skipped in 3s

1 files ±0 12 suites ±0 3s ⏱️ ±0s
149 tests ±0 146 ✅ ±0 3 💤 ±0 0 ❌ ±0
229 runs ±0 226 ✅ ±0 3 💤 ±0 0 ❌ ±0

Results for commit 7b8e1cb. ± Comparison against earlier commit 40385ba.