Use HTTPS instead of HTTP to resolve dependencies (#448)

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

@@ -477,7 +477,7 @@
   <repositories>
     <repository>
       <id>repo.jenkins-ci.org</id>
-      <url>http://repo.jenkins-ci.org/public/</url>
+      <url>https://repo.jenkins-ci.org/public/</url>
     </repository>
   </repositories>