Update source level to Java 8
diff --git a/pom.xml b/pom.xml
index 9a14682..4f3b4ed 100644
--- a/pom.xml
+++ b/pom.xml
@@ -1329,8 +1329,8 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <inherited>true</inherited>
                 <configuration>
-                    <source>1.7</source>
-                    <target>1.7</target>
+                    <source>1.8</source>
+                    <target>1.8</target>
                 </configuration>
             </plugin>
             <plugin>
@@ -1349,7 +1349,7 @@
                 <configuration>
                     <signature>
                         <groupId>org.codehaus.mojo.signature</groupId>
-                        <artifactId>java17</artifactId>
+                        <artifactId>java18</artifactId>
                         <version>1.0</version>
                     </signature>
                 </configuration>