Use higher resolution marketplace install button

Related to https://bugs.eclipse.org/bugs/show_bug.cgi?id=565317

README.md

@@ -51,7 +51,7 @@ Check out what's new in the [latest releases](https://github.com/PyvesB/eclipse-
 You can download and install the plugin via the [Eclipse Marketplace](https://marketplace.eclipse.org/content/ruby-solargraph/), or simply drag the below button to your running Eclipse workspace:
 
 <p align="center">
-<a href="http://marketplace.eclipse.org/marketplace-client-intro?mpc_install=4611382" class="drag" title="Drag to your running Eclipse workspace. Requires Eclipse Marketplace Client"><img typeof="foaf:Image" class="img-responsive" src="https://marketplace.eclipse.org/sites/all/themes/solstice/public/images/marketplace/btn-install.png" alt="Drag to your running Eclipse workspace. Requires Eclipse Marketplace Client" /></a>
+<a href="http://marketplace.eclipse.org/marketplace-client-intro?mpc_install=4611382" class="drag" title="Drag to your running Eclipse* workspace. *Requires Eclipse Marketplace Client"><img style="width:80px;" typeof="foaf:Image" class="img-responsive" src="https://marketplace.eclipse.org/sites/all/themes/solstice/public/images/marketplace/btn-install.svg" alt="Drag to your running Eclipse* workspace. *Requires Eclipse Marketplace Client" /></a>
 </p>
 
 Alternatively, head to the [update site](https://pyvesb.github.io/eclipse-solargraph/) and follow the instructions listed there.