Fix an accidental escape sequence in a unit test

This amends b49ce9c

Author: AaronBallman

clang/unittests/Driver/DXCModeTest.cpp

@@ -158,7 +158,7 @@ TEST(DxcModeTest, ValidatorVersionValidation) {
   EXPECT_EQ(Diags.getNumErrors(), 1u);
   EXPECT_STREQ(
       DiagConsumer->Errors.back().c_str(),
-      "invalid validator version : 0.1\; if validator major version is 0, "
+      "invalid validator version : 0.1; if validator major version is 0, "
       "minor version must also be 0");
   Diags.Clear();
   DiagConsumer->clear();