Release 1.5.8.1, pom fix attempt, Jitpack release failed so this shou…

…ld fix it

pom.xml

@@ -7,6 +7,28 @@
     <groupId>io.github.retrooper</groupId>
     <artifactId>packetevents</artifactId>
     <version>1.5.8</version>
+
+    <!-- You can build the project with this: "mvn clean compile assembly:single" -->
+    <build>
+        <plugins>
+            <plugin>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <configuration>
+                    <descriptorRefs>
+                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                    </descriptorRefs>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>8</source>
+                    <target>8</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
     <packaging>jar</packaging>
     <name>packetevents</name>