Use a dedicated format to save lock status

[kana]

Lock status is currently written in YAML. But the YAML module included in the standard library might write different text between different Ruby versions. See below for an example. Use a dedicated format to avoid such unnecessary changes.

diff --git a/vim/VimFlavor.lock b/vim/VimFlavor.lock
index de00c5b..df9ff93 100644
--- a/vim/VimFlavor.lock
+++ b/vim/VimFlavor.lock
@@ -1,242 +1,282 @@
----
-:flavors:
-  git://github.com/kana/vim-altercmd.git:
-    :groups:
+---
+:flavors:
+  git://github.com/kana/vim-altercmd.git:
+    :groups:
     - :default
     :locked_version: 0.0.0
-    :repo_name: kana/vim-altercmd
-    :version_contraint: ">= 0"
-  git://github.com/kana/vim-altr.git:
-    :groups:
+    :repo_name: !binary |-
+      a2FuYS92aW0tYWx0ZXJjbWQ=
+    :version_contraint: ! '>= 0'
+  git://github.com/kana/vim-altr.git:
+    :groups:
     - :default
     :locked_version: 0.0.1

[kana]

$repo_name ($locked_version)
  $required_repo_name ($version_constraint)
  ...
...