Update CHANGELOG for the 3.7.3 release

CHANGELOG.md

@@ -5,6 +5,7 @@
 _Released: 2018-01-19_
 
  * In rare cases, when using `glob()` to find `/sys/class/net/*/address` files on Linux, `glob()` encountered errors, returning `false` instead of an empty array, causing `array_map()` to emit warnings since its second parameter was not an array; this release gracefully handles cases where `glob()` returns `false` [#203](https://github.com/ramsey/uuid/issues/203)
+ * Fixed an off-by-one error in `DefaultTimeGenerator` and switching to `random_int()` from `mt_rand()` for better random numbers [#206](https://github.com/ramsey/uuid/pull/206)
 
 ## 3.7.2