bump plugins and a dependency

pom.xml

@@ -41,6 +41,10 @@
     </developer>
   </developers>
 
+  <prerequisites>
+    <maven>3.0.4</maven>
+  </prerequisites>
+
   <dependencies>
     <dependency>
       <groupId>com.squareup.okhttp</groupId>
@@ -55,7 +59,7 @@
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
-      <version>4.11</version>
+      <version>4.12</version>
       <scope>test</scope>
     </dependency>
     <dependency>
@@ -110,7 +114,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-gpg-plugin</artifactId>
-        <version>1.5</version>
+        <version>1.6</version>
         <executions>
           <execution>
             <id>sign-artifacts</id>
@@ -124,7 +128,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-source-plugin</artifactId>
-        <version>2.2.1</version>
+        <version>2.4</version>
         <executions>
           <execution>
             <id>attach-sources</id>
@@ -137,7 +141,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-javadoc-plugin</artifactId>
-        <version>2.9.1</version>
+        <version>2.10.3</version>
         <executions>
           <execution>
             <id>attach-javadocs</id>
@@ -161,7 +165,7 @@
       <plugin>
         <groupId>org.sonatype.plugins</groupId>
         <artifactId>nexus-staging-maven-plugin</artifactId>
-        <version>1.6.2</version>
+        <version>1.6.6</version>
         <extensions>true</extensions>
         <configuration>
           <serverId>ossrh</serverId>
@@ -172,7 +176,7 @@
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>exec-maven-plugin</artifactId>
-        <version>1.2.1</version>
+        <version>1.4.0</version>
         <executions>
           <execution>
             <id>npm-install</id>