fix(2019/day/9): TS2870

> [ERROR]: This binary expression is never nullish. Are you missing parentheses?

Author: mfulton26

2019/day/9/part/1/solve.ts

@@ -32,7 +32,7 @@ function program(memory: number[]) {
               position = instructionPointer++;
               break;
             case 2:
-              position = relativeBase + memory[instructionPointer++] ?? 0;
+              position = relativeBase + (memory[instructionPointer++] ?? 0);
               break;
             default:
               throw new Error("unreachable");