Fix typo in spec file description [ci skip]

fixed typo for spec description

Author: Ivanov-Anton

spec/ruby/shared/rational/truncate.rb

@@ -55,7 +55,7 @@
     end
   end
 
-  describe "with an invalid valud for precision" do
+  describe "with an invalid value for precision" do
     it "raises a TypeError" do
       -> { @rational.truncate(nil) }.should raise_error(TypeError, "not an integer")
       -> { @rational.truncate(1.0) }.should raise_error(TypeError, "not an integer")