Reduce concurrent requests

Countdown API limits requests, so reducing this value from 6 -> 2
reduces the chance of bad API responses.

In the future, we should implement retry, and also not crash the first
time we fail to collect a price. Our scraper should be resilient and
continue to scrape, reporting the failures at the end.

src/lib.rs

@@ -12,4 +12,4 @@ pub const CACHE_PATH: &str = "cache.json";
 /// The amount of milliseconds to wait between performing iterations on the pages.
 pub const PAGE_ITERATION_INTERVAL: Duration = Duration::from_millis(500);
 /// The amount of requests to perform in parallel.
-pub const CONCURRENT_REQUESTS: i64 = 6;
+pub const CONCURRENT_REQUESTS: i64 = 2;