source compatibility still java 8

We aren't sure what to do with Java versions yet, so I'm setting
source compatibility to Java 8 until we figure it out.

buildSrc/src/main/kotlin/com/dfsek/terra/CompilationConfig.kt

@@ -14,7 +14,7 @@ fun Project.configureCompilation() {
     apply(plugin = "idea")
 
     configure<JavaPluginConvention> {
-        sourceCompatibility = JavaVersion.VERSION_16
+        sourceCompatibility = JavaVersion.VERSION_1_8
         targetCompatibility = JavaVersion.VERSION_16
     }