Exclude test for sprintf %f formatting of Rational. #2160

Author: headius

test/mri/excludes/TestSprintf.rb

@@ -8,4 +8,5 @@
 exclude :test_named_untyped, "needs investigation"
 exclude :test_named_untyped_enc, "needs investigation"
 exclude :test_nan, "needs investigation"
+exclude :test_rational, "missing special rational handling in sprintf (#2160)"
 exclude :test_star, "differing error message somewhere deep in GETNUM macro from MRI and our equivalents"