[Optimize]add generics for CacheBuilder

[onewe]

I think some methods of the CacheBuilder need to add the generics.

for example:

// CacheBuilder#builder:51
    public static CacheBuilder builder() {
        return new CacheBuilder();
    }

and here:

// CacheBuilder#builder:58
 public CacheBuilder expireNanos(long duration, TimeUnit unit) {
        checkExpireNanos(duration, unit);
        this.expireNanos = unit.toNanos(duration);
        return this;
    }