make tests pass under Ruby 2.1

spec/fixtures/mark1.yml

@@ -2,41 +2,41 @@
 :-:
   0----:
     :next_state: :state1
-    :output: -11---1-00------
+    :output: "-11---1-00------"
 :state1:
   1----:
     :next_state: :state3
-    :output: -11---1-00------
+    :output: "-11---1-00------"
 :state2:
   1----:
     :next_state: :state0
-    :output: -11---1-00------
+    :output: "-11---1-00------"
 :state3:
   1----:
     :next_state: :state4
     :output: 101---1-01------
 :state4:
   1-111:
     :next_state: :state13
-    :output: -11---1-00------
+    :output: "-11---1-00------"
   1-110:
     :next_state: :state10
-    :output: -11---1-00------
+    :output: "-11---1-00------"
   1-10-:
     :next_state: :state9
-    :output: -11---1-00------
+    :output: "-11---1-00------"
   1-011:
     :next_state: :state8
-    :output: -11---1-00------
+    :output: "-11---1-00------"
   1-010:
     :next_state: :state7
-    :output: -11---1-00------
+    :output: "-11---1-00------"
   1-001:
     :next_state: :state6
-    :output: -11---1-00------
+    :output: "-11---1-00------"
   1-000:
     :next_state: :state5
-    :output: -11---1-00------
+    :output: "-11---1-00------"
 :state5:
   1----:
     :next_state: :state14
@@ -60,27 +60,27 @@
 :state10:
   1----:
     :next_state: :state11
-    :output: -11---1-00100000
+    :output: "-11---1-00100000"
 :state11:
   10---:
     :next_state: :state13
-    :output: -11---1-00------
+    :output: "-11---1-00------"
   11---:
     :next_state: :state12
-    :output: -11---1-00------
+    :output: "-11---1-00------"
 :state12:
   1----:
     :next_state: :state13
-    :output: -110110-00------
+    :output: "-110110-00------"
 :state13:
   1----:
     :next_state: :state14
-    :output: -11---1-00------
+    :output: "-11---1-00------"
 :state14:
   1----:
     :next_state: :state3
-    :output: -110110-00------
+    :output: "-110110-00------"
 :state0:
   0----:
     :next_state: :state1
-    :output: -11---1-00------
+    :output: "-11---1-00------"