Fix compiler.close() in CompilerTest

Since the compiler is instantiated on class level, it should also be
torn down on class level.

server/src/test/kotlin/org/javacs/kt/CompilerTest.kt

@@ -35,6 +35,7 @@ private class FileToEdit {
 
         @JvmStatic @AfterClass
         fun tearDown() {
+            compiler.close()
             outputDirectory.delete()
         }
     }
@@ -89,8 +90,4 @@ private class FileToEdit {
 
         assertThat(target.name, hasToString("intFunction"))
     }
-
-    @After fun cleanUp() {
-        compiler.close()
-    }
 }