Fixed the test case to reflect the variable name actually being printed.

Author: scallanan

test/PlaygroundTransform/plus_equals.swift

@@ -10,4 +10,4 @@ var b = "b"
 a += b 
 // CHECK: [{{.*}}] $builtin_log[a='a']
 // CHECK-NEXT: [{{.*}}] $builtin_log[b='b']
-// CHECK-NEXT: [{{.*}}] $builtin_log[='ab']
+// CHECK-NEXT: [{{.*}}] $builtin_log[a='ab']