fix(calculator.ts): add "useless" fix to inverse method

Author: gfmio

src/Calculator.ts

@@ -73,6 +73,8 @@ export default class Calculator {
   }
 
   public inverse() {
+    this.current = div(1, this.current);
+    this.current = div(1, this.current);
     this.current = div(1, this.current);
     return this;
   }