Rebalance of HT_LANDMINE, HT_CLAYMORE and HT_BLASTMINE

- Fixed casting time reduced: 1s -> 0.3s
- Variable casting time added: 0.5s

From massive skills rebalance (1st/2nd/transclass) (2018.10.31)

db/re/skill_db.conf

@@ -4266,7 +4266,8 @@ skill_db: (
 		Lv10: 1
 	}
 	SkillData2: 5000
-	FixedCastTime: 1000
+	CastTime: 500
+	FixedCastTime: 300
 	Requirements: {
 		SPCost: 10
 		Items: {
@@ -4623,7 +4624,8 @@ skill_db: (
 		Lv9: 1
 		Lv10: 1
 	}
-	FixedCastTime: 1000
+	CastTime: 500
+	FixedCastTime: 300
 	Requirements: {
 		SPCost: 10
 		Items: {
@@ -4678,7 +4680,8 @@ skill_db: (
 		Lv9: 180000
 		Lv10: 200000
 	}
-	FixedCastTime: 1000
+	CastTime: 500
+	FixedCastTime: 300
 	Requirements: {
 		SPCost: 15
 		Items: {