Fix coveralls upload on Travis, use SVG badge.

Coverage upload failed because of:
trautonen/coveralls-maven-plugin#127

README.md

@@ -2,7 +2,7 @@ Wikidata Toolkit
 ================
 
 [![Build Status](https://travis-ci.org/Wikidata/Wikidata-Toolkit.png?branch=master)](https://travis-ci.org/Wikidata/Wikidata-Toolkit)
-[![Coverage Status](https://coveralls.io/repos/Wikidata/Wikidata-Toolkit/badge.png?branch=master)](https://coveralls.io/r/Wikidata/Wikidata-Toolkit?branch=master)
+[![Coverage Status](https://coveralls.io/repos/github/Wikidata/Wikidata-Toolkit/badge.svg?branch=master)](https://coveralls.io/github/Wikidata/Wikidata-Toolkit?branch=master)
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/org.wikidata.wdtk/wdtk-parent/badge.svg)](http://search.maven.org/#search|ga|1|g%3A%22org.wikidata.wdtk%22)
 [![Project Stats](https://www.openhub.net/p/Wikidata-Toolkit/widgets/project_thin_badge.gif)](https://www.openhub.net/p/Wikidata-Toolkit)
 

pom.xml

@@ -186,7 +186,7 @@
 				<!-- Create code coverage reports and submit them to coveralls.io. -->
 				<groupId>org.eluder.coveralls</groupId>
 				<artifactId>coveralls-maven-plugin</artifactId>
-				<version>4.3.0</version>
+				<version>2.1.0</version>
 			</plugin>
 			<plugin>
 				<!-- Plugin for actually computing code coverage. -->