[fix] make FunctionCache thread safe

src/main/kotlin/ru/inr/mass/trapping/FunctionCache.kt

@@ -10,7 +10,9 @@ class FunctionCache(private val xPrecision: Double, val function: (Double) -> Do
         val ceil: MutableMap.MutableEntry<Double, Double>? = values.ceilingEntry(x)
         return if (floor == null || ceil == null || ceil.key - floor.key <= xPrecision) {
             val newValue = function(x)
-            values[x] = newValue
+            synchronized(this) {
+                values[x] = newValue
+            }
             newValue
         } else {
             val x0 = floor.key