feat: update inequality in step 5.4

This patch follows the 2022-03-22 update to the Glicko-2 algorithm:

    This document has been revised on March 22, 2022, to replace a "<"
    with "<=" in item 4(b) of Step 5 (page 3).

index.js

@@ -142,7 +142,7 @@ function computeVolatility(sigma, phi, v, delta, options) {
     const c = a + (a - b) * fa / (fb - fa);
     const fc = f(c);
 
-    if (fc * fb < 0) {
+    if (fc * fb <= 0) {
       a = b;
       fa = fb;
     }