Add scala-compiler dependency to fix Scala dev mode recompilation.

Using a different version of Scala than Quarkus' internal
${scala.version} breaks dev mode.  Adding an explicit scala-compiler
dependency fixes it again.

Change-Id: I6fb2b748fd4bbbb15e32ccd42c674f67551e9411
diff --git a/pom.xml b/pom.xml
index 44ee46f..a5f0fde 100644
--- a/pom.xml
+++ b/pom.xml
@@ -136,6 +136,11 @@
       <artifactId>scala-reflect</artifactId>
       <version>${scala.version}</version>
     </dependency>
+    <dependency>
+      <groupId>org.scala-lang</groupId>
+      <artifactId>scala-compiler</artifactId>
+      <version>${scala.version}</version>
+    </dependency>
 
     <dependency>
       <groupId>io.quarkus</groupId>