Merge pull request #66 from intuit/fix_ci

Fix ci - tests failed due to "PluginException - Cannot distinguish StubFileElementTypes"

src/main/kotlin/name/kropp/intellij/makefile/MakefileStubFileElementType.kt

@@ -3,4 +3,8 @@ package name.kropp.intellij.makefile
 import com.intellij.psi.stubs.PsiFileStub
 import com.intellij.psi.tree.IStubFileElementType
 
-class MakefileStubFileElementType : IStubFileElementType<PsiFileStub<MakefileFile>>(MakefileLanguage)
+class MakefileStubFileElementType : IStubFileElementType<PsiFileStub<MakefileFile>>(MakefileLanguage) {
+    override fun getExternalId(): String {
+        return "makefile.FILE"
+    }
+}