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

@@ -149,7 +149,7 @@
         </repository>
         <repository>
             <id>sk89q-repo</id>
-            <url>http://maven.sk89q.com/repo/</url>
+            <url>https://maven.sk89q.com/repo/</url>
         </repository>
     </repositories>
     <dependencies>