Upgrade leshan dependencies

pom.xml

@@ -110,8 +110,8 @@ Contributors:
         <!-- dependencies version -->
         <californium.version>2.0.0</californium.version>
         <logback.version>1.2.3</logback.version>
-        <slf4j.api.version>1.7.25</slf4j.api.version>
-        <jetty.version>9.1.4.v20140401</jetty.version>
+        <slf4j.api.version>1.7.30</slf4j.api.version>
+        <jetty.version>9.4.26.v20200117</jetty.version>
     </properties>
 
     <distributionManagement>
@@ -229,6 +229,11 @@ Contributors:
                 <plugin>
                     <artifactId>maven-enforcer-plugin</artifactId>
                     <version>1.4.1</version>
+                </plugin>
+                 <plugin>
+                    <groupId>org.codehaus.mojo</groupId>
+                    <artifactId>versions-maven-plugin</artifactId>
+                    <version>2.7</version>
                 </plugin>
                 <plugin>
                     <groupId>org.sonatype.plugins</groupId>
@@ -518,7 +523,7 @@ Contributors:
             <dependency>
                 <groupId>com.google.code.gson</groupId>
                 <artifactId>gson</artifactId>
-                <version>2.2.4</version>
+                <version>2.8.6</version>
             </dependency>
             <dependency>
                 <groupId>commons-lang</groupId>
@@ -528,12 +533,12 @@ Contributors:
             <dependency>
                 <groupId>commons-io</groupId>
                 <artifactId>commons-io</artifactId>
-                <version>2.4</version>
+                <version>2.6</version>
             </dependency>
             <dependency>
                 <groupId>commons-cli</groupId>
                 <artifactId>commons-cli</artifactId>
-                <version>1.3.1</version>
+                <version>1.4</version>
             </dependency>
             <dependency>
                 <groupId>org.eclipse.jetty</groupId>
@@ -550,13 +555,7 @@ Contributors:
             <dependency>
                 <groupId>junit</groupId>
                 <artifactId>junit</artifactId>
-                <version>4.12</version>
-                <scope>test</scope>
-            </dependency>
-            <dependency>
-                <groupId>org.mockito</groupId>
-                <artifactId>mockito-all</artifactId>
-                <version>1.9.5</version>
+                <version>4.13</version>
                 <scope>test</scope>
             </dependency>
         </dependencies>