(TK-88) Removed errant build call from JavaClient's createClient()

This commit removes an unnecessary build() method call made on the
HttpAsyncClientBuilder in JavaClient's createClient() method.
Previously, the presence of this call would cause an extra
CloseableHttpAsyncClient object to be created.  Since close() was never
called on the extra client object, native file descriptor resources were
never freed even after the object fell out of scope.
Merge pull request #18 from camlow325/bug/master/TK-88-errant-client-build

(TK-88) Removed errant build call from JavaClient's createClient()
Updated changelog for 0.2.8 release
Merge pull request #19 from camlow325/maint/master/clj-http-client-0.2.8-release

Updated changelog for 0.2.8 release
lein-release plugin: preparing 0.2.8 release
lein-release plugin: bumped version from 0.2.8 to 0.2.9-SNAPSHOT for next development cycle