Fix typo in CheckDiscardDiagnostic error message.

s/where/were/

Change-Id: Ic098ea48c06294b70382ed0e05f2821d0afdbf46
diff --git a/src/main/java/com/android/tools/r8/errors/CheckDiscardDiagnostic.java b/src/main/java/com/android/tools/r8/errors/CheckDiscardDiagnostic.java
index ce54533..5a9ebb3 100644
--- a/src/main/java/com/android/tools/r8/errors/CheckDiscardDiagnostic.java
+++ b/src/main/java/com/android/tools/r8/errors/CheckDiscardDiagnostic.java
@@ -66,7 +66,7 @@
     StringBuilder builder = new StringBuilder("Discard checks failed.");
     if (messages.size() > 0) {
       builder.append(System.lineSeparator());
-      builder.append("The following items where not discarded");
+      builder.append("The following items were not discarded");
       messages.forEach(
           message -> {
             builder.append(System.lineSeparator());