Update mastodon dep version.

Author: tinevez

pom.xml

@@ -101,7 +101,7 @@
 		<license.organizationName>Mastodon authors</license.organizationName>
 		<license.copyrightOwners>Tobias Pietzsch, Jean-Yves Tinevez</license.copyrightOwners>
 
-		<mastodon.version>1.0.0-beta-27</mastodon.version>
+		<mastodon.version>1.0.0-beta-29</mastodon.version>
 		<mastodon-tracking.version>1.0.0-beta-14</mastodon-tracking.version>
 
 		<!-- NB: Deploy releases to the SciJava Maven repository. -->