Don't use deprecated+deleted Google Truth `fail` method

Summary: The `fail` method we previously used was deprecated and removed.

Reviewed By: strulovich

Differential Revision: D19195985

fbshipit-source-id: 026ea1ea860691dcf25633981a6a4d527005dd1c

core/src/test/java/com/facebook/ktfmt/FormatterKtTest.kt

diff --git a/core/src/test/java/com/facebook/ktfmt/FormatterKtTest.kt b/core/src/test/java/com/facebook/ktfmt/FormatterKtTest.kt
index d685878..cf2c3f5 100644
--- a/core/src/test/java/com/facebook/ktfmt/FormatterKtTest.kt
+++ b/core/src/test/java/com/facebook/ktfmt/FormatterKtTest.kt
@@ -1607,7 +1607,7 @@
     fun isEqualTo(expectedFormatting: String) {
       val code = actual()
       if (expectedFormatting.lines().any { it.endsWith(" ") }) {
-        fail(
+        throw RuntimeException(
             "Expected code contains trailing whitespace, which the formatter will never output:\n" +
                 expectedFormatting.lines().map { if (it.endsWith(" ")) "[$it]" else it }.joinToString("\n"))
       }