Fix the issue lookback duration to be 90 days. (#605)

Signed-off-by: Caleb Brown <calebbrown@google.com>

internal/collector/github/legacy/constants.go

@@ -21,7 +21,7 @@ import (
 
 const (
 	SinceDuration time.Duration = time.Hour * 24 * 30
-	IssueLookback time.Duration = time.Hour * 24 * 90 * 24
+	IssueLookback time.Duration = time.Hour * 24 * 90
 
 	// TODO: these limits should ultimately be imposed by the score generation, not here.
 	MaxContributorLimit = 5000