Use HTTPS instead of HTTP to resolve dependencies

This fixes a security vulnerability in this project where the `pom.xml`
files were configuring Maven to resolve dependencies over HTTP instead of
HTTPS.

Signed-off-by: Jonathan Leitschuh <Jonathan.Leitschuh@gmail.com>

pom.xml

@@ -98,7 +98,7 @@
     <pluginRepositories>
         <pluginRepository>
             <id>sonatype-public</id>
-            <url>http://repository.sonatype.org/content/groups/sonatype-public-grid</url>
+            <url>https://repository.sonatype.org/content/groups/sonatype-public-grid</url>
             <snapshots>
                 <enabled>true</enabled>
             </snapshots>