"Mongolian Vowel Separator" is not considered whitespace after Ruby 2.2

[Ruby Issue 9092](https://bugs.ruby-lang.org/issues/9092) updated Ruby from Unicode 6.1 to Unicode 7.0 ([commit here](ruby/ruby@64c81e4#diff-67d181a69374a75e4b8f706fa9b81fbc)).  This patch was included in Ruby 2.2.

From the [Unicode 6.3.0 release notes](http://www.unicode.org/versions/Unicode6.3.0/):

    The General_Category property value of U+180E MONGOLIAN VOWEL SEPARATOR has been changed from Zs to Cf. The values of other related properties such as Bidi_Class, White_Space, and Other_Default_Ignorable_Code_Point have been updated accordingly.

After 2.2 shipped, Ruby's [[:space:]] Regexp expression [no longer matches U+180E](https://github.com/ruby/ruby/blob/9fefa6063797f94704c09663db13cea9e390eaba/enc/unicode/name2ctype.h#L2740-L2753).

This updates fast_blank to treat U+180E properly in blank_as?

Prior to this change, the tests fail on 2.2.2:

    1) String provides a parity with active support function
       Failure/Error: expect("#{i.to_s(16)} #{c.blank_as?}").to eq("#{i.to_s(16)} #{c.blank2?}")
    -
         expected: "180e false"
              got: "180e true"
    -
         (compared using ==)
       # ./spec/fast_blank_spec.rb:22:in `block (3 levels) in <top (required)>'
       # ./spec/fast_blank_spec.rb:19:in `times'
       # ./spec/fast_blank_spec.rb:19:in `block (2 levels) in <top (required)>'

It now passes on all the Rubies in the Travis matrix (RBX, 1.9, 2.0, 2.1, and 2.2).

.travis.yml

@@ -1,5 +1,6 @@
 language: ruby
 rvm:
+  - 2.2.2
   - 2.1.6
   - 2.0.0
   - 1.9.3

ext/fast_blank/fast_blank.c

@@ -2,6 +2,7 @@
 #include <ruby.h>
 #include <ruby/encoding.h>
 #include <ruby/re.h>
+#include <ruby/version.h>
 
 #define STR_ENC_GET(str) rb_enc_from_index(ENCODING_GET(str))
 
@@ -13,6 +14,17 @@
 #define RSTRING_LEN(s) (RSTRING(s)->len)
 #endif
 
+static int
+ruby_version_before_2_2()
+{
+  #ifdef RUBY_API_VERSION_MAJOR
+  if (RUBY_API_VERSION_MAJOR > 2 || (RUBY_API_VERSION_MAJOR == 2 && RUBY_API_VERSION_MINOR >= 2)) {
+    return 0;
+  }
+  #endif
+  return 1;
+}
+
 static VALUE
 rb_str_blank_as(VALUE str)
 {
@@ -38,7 +50,6 @@ rb_str_blank_as(VALUE str)
       case 0x85:
       case 0xa0:
       case 0x1680:
-      case 0x180e:
       case 0x2000:
       case 0x2001:
       case 0x2002:
@@ -57,6 +68,8 @@ rb_str_blank_as(VALUE str)
       case 0x3000:
           /* found */
           break;
+      case 0x180e:
+          if (ruby_version_before_2_2()) break;
       default:
           return Qfalse;
     }