Switch to -SNAPSHOT version of Fernflower

Local variable name tracking with the @Pc annotation relies on changes
not yet included in a release. I'm not intending to do another
Fernflower release yet, as I've still got more changes to make, but I
would like the @Pc tracking to work.

Signed-off-by: Graham <gpe@openrs2.dev>

buildSrc/src/main/java/Versions.kt

@@ -5,7 +5,7 @@ object Versions {
     const val commonsCompress = "1.20"
     const val dependencyLicenseReport = "1.13"
     const val fastutil = "8.3.1"
-    const val fernflower = "1.0.3"
+    const val fernflower = "1.0.4-SNAPSHOT"
     const val guava = "29.0-jre"
     const val guice = "4.2.3"
     const val inlineLogger = "1.0.2"