update CHANGELOG and bump version to 5.8.1

Author: beniwohli

CHANGELOG.asciidoc

@@ -30,23 +30,18 @@ endif::[]
 //===== Bug fixes
 //
 
-=== Unreleased
-
-// Unreleased changes go here
-// When the next release happens, nest these changes under the "Python Agent version 5.x" heading
-[float]
-===== Features
+[[release-notes-5.x]]
+=== Python Agent version 5.x
 
+[[release-notes-5.8.1]]
+==== v5.8.1
 
 [float]
 ===== Bug fixes
 
 * Updated CLOUD_PROVIDER config to allow for new options defined in https://github.com/elastic/apm/issues/289[#289] {pull}878[#878]
 * Fixed a bug in AWS metadata collection on docker containers in AWS Elastic Beanstalk {pull}884[#884]
-
-
-[[release-notes-5.x]]
-=== Python Agent version 5.x
+* Fixed a bug in local variable serialization that could occur in multi-threaded applications {pull}885[#885] 
 
 [[release-notes-5.8.0]]
 ==== v5.8.0

elasticapm/version.py

@@ -28,5 +28,5 @@
 #  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 #  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-__version__ = (5, 8, 0)
+__version__ = (5, 8, 1)
 VERSION = ".".join(map(str, __version__))