Small typo in Phi error message

Change-Id: If177b682c158df6ee5970beedeccae1b51d8d845
diff --git a/src/main/java/com/android/tools/r8/ir/code/Phi.java b/src/main/java/com/android/tools/r8/ir/code/Phi.java
index 2d45303..c0dac12 100644
--- a/src/main/java/com/android/tools/r8/ir/code/Phi.java
+++ b/src/main/java/com/android/tools/r8/ir/code/Phi.java
@@ -159,7 +159,7 @@
     throw new CompilationError(
         "Undefined value encountered during compilation. "
             + "This is typically caused by invalid dex input that uses a register "
-            + "that is not define on all control-flow paths leading to the use.");
+            + "that is not defined on all control-flow paths leading to the use.");
   }
 
   private void appendOperand(Value operand) {