Remove trailing slashes from repository specifications.

The correct format is to not have a trailing slash.

For me this caused non-deterministic failures due to issues fetching
certain artifacts. The issue was that some of the maven caches would
fail to fetch the artifact (due to the way that the artifact
path was concatenated with the repository) and this short-circuited
the download process in a silent way. Here is what the log output
looked like:

    Downloading: http://repo.maven.apache.org/maven2/org/spark-project/akka/akka-remote_2.10/2.2.3-shaded-protobuf/akka-remote_2.10-2.2.3-shaded-protobuf.pom
    [WARNING] The POM for org.spark-project.akka:akka-remote_2.10:jar:2.2.3-shaded-protobuf is missing, no dependency information available

This was pretty brutal to debug since there was no error message
anywhere and the path *looks* correct as reported by the Maven log.

pom.xml

@@ -120,7 +120,7 @@
     <repository> 
       <id>maven-repo</id> <!-- This should be at top, it makes maven try the central repo first and then others and hence faster dep resolution -->
       <name>Maven Repository</name>
-      <url>http://repo.maven.apache.org/maven2/</url>
+      <url>http://repo.maven.apache.org/maven2</url>
       <releases>
         <enabled>true</enabled>
       </releases>
@@ -131,7 +131,7 @@
     <repository>
       <id>jboss-repo</id>
       <name>JBoss Repository</name>
-      <url>http://repository.jboss.org/nexus/content/repositories/releases/</url>
+      <url>http://repository.jboss.org/nexus/content/repositories/releases</url>
       <releases>
         <enabled>true</enabled>
       </releases>
@@ -142,7 +142,7 @@
     <repository>
       <id>mqtt-repo</id>
       <name>MQTT Repository</name>
-      <url>https://repo.eclipse.org/content/repositories/paho-releases/</url>
+      <url>https://repo.eclipse.org/content/repositories/paho-releases</url>
       <releases>
         <enabled>true</enabled>
       </releases>
@@ -739,7 +739,7 @@
         <repository>
           <id>maven-root</id>
           <name>Maven root repository</name>
-          <url>http://repo1.maven.org/maven2/</url>
+          <url>http://repo1.maven.org/maven2</url>
           <releases>
             <enabled>true</enabled>
           </releases>
@@ -771,7 +771,7 @@
          <repository>
            <id>maven-root</id>
            <name>Maven root repository</name>
-           <url>http://repo1.maven.org/maven2/</url>
+           <url>http://repo1.maven.org/maven2</url>
            <releases>
              <enabled>true</enabled>
            </releases>