variance is imprecise when size is small (Netflix#418)

In my opinion the current variance (and by consequence
the standard deviation) computation are imprecise, when
curSize is not high (when curSize < 10 for example):

```java
    variance = (sumSquares / curSize) - (mean * mean);
```

The computation I suggest in this pull request does not hurt
and is precise:

```java
    if (curSize == 1) {
      variance = 0d;
    } else {
      variance = (sumSquares - ((double) total * total / curSize)) / (curSize - 1);
    }
```

For reference:
http://web.archive.org/web/20050512031826/http://helios.bto.ed.ac.uk/bto/statistics/tress3.html

v0.12.15

* Updated AWS SDK dependencies

v0.12.14

* Atlas validation rules for groups

v0.12.13

* Reduce garbage generated in `ValidCharacters#toValidCharset`
* MonitorTags annotation support from parent classes
* Style fixes

reduce thread contention for expiring cache

update to netty-4.1.5 (Netflix#398)

This version has a fix needed to coexist with apps
running in tomcat with tomcat-native.

fix missing dependency error due to bad pom (Netflix#394)

iepshadow-iep-rxhttp 0.4.6.26 is published with a missing
dependency in the pom. Fixed in 0.4.6.27.

Merge pull request Netflix#393 from brharrington/fix-guice

update iep shadow to fix bad guice version