Fix gcd

Author: ta7uw

lib/number/lcm.cpp

@@ -1,7 +1,6 @@
 ll gcd(ll a, ll b) {
-    if (a < b)swap(a, b);
-    if (b == 0)return a;
-    return gcd(b, a % b);
+    if (b == 0) return a;
+    else return gcd(b, a % b);
 }
 
 ll lcm(ll a, ll b) {