Fix Rules-initialWaveSpacing comment (#7093)

(In fact I'm not sure if this should be edited to "<=0" to correspond with the actual codes.

core/src/mindustry/game/Rules.java

@@ -94,7 +94,7 @@ public class Rules{
     public float dropZoneRadius = 300f;
     /** Time between waves in ticks. */
     public float waveSpacing = 2 * Time.toMinutes;
-    /** Starting wave spacing; if <0, uses waveSpacing * 2. */
+    /** Starting wave spacing; if <=0, uses waveSpacing * 2. */
     public float initialWaveSpacing = 0f;
     /** Wave after which the player 'wins'. Used in sectors. Use a value <= 0 to disable. */
     public int winWave = 0;