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>
diff --git a/pom.xml b/pom.xml
index b31764f..b074bcf 100644
--- a/pom.xml
+++ b/pom.xml
@@ -328,7 +328,7 @@
     <pluginRepository>
       <id>apache.snapshots</id>
       <name>Apache Snapshot Repository</name>
-      <url>http://repository.apache.org/snapshots</url>
+      <url>https://repository.apache.org/snapshots</url>
       <releases>
         <enabled>false</enabled>
       </releases>