Correct region to avoid exception upon startup

[eddgrant]

README.me gives an example region of EU_WEST_1 however this causes the following exception upon startup:

Caused by: java.lang.IllegalArgumentException: The region 'EU_WEST_1' is not a valid region!
  at org.springframework.util.Assert.notNull(Assert.java:112)
  at org.springframework.cloud.aws.core.region.StaticRegionProvider.<init>(StaticRegionProvider.java:44)
  at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
  at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
  at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
  at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
  at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:147)
  ... 59 more

StaticRegionProvider uses RegionUtils which, by default, takes its regions from /com/amazonaws/regions/regions.xml. In here the correct region name is eu-west-1.

Updated README.md to reflect this and have tested the change locally with success.