Adjusted test cases due to change in directive parsing.

We changed the structure of the regex to be a little less flexible, so
we adjust our test examples to match the updated format.

i18n-helpers/src/bin/mdbook-xgettext.rs

@@ -303,10 +303,10 @@ mod tests {
             (
                 "src/foo.md",
                 "
-<!-- mdbook-xgettext-comment: This is a header. -->
+<!-- mdbook-xgettext:comment: This is a header. -->
 # How to Foo
 
-<!-- mdbook-xgettext-comment: I am a comment. -->
+<!-- mdbook-xgettext:comment: I am a comment. -->
 The first paragraph about Foo.
 Still the first paragraph.
 ",

i18n-helpers/src/lib.rs

@@ -1585,7 +1585,7 @@ def g(x):
         assert_eq!(
             extract_messages(
                 "
-<!-- mdbook-xgettext-comment: first comment! -->
+<!-- mdbook-xgettext:comment: first comment! -->
 Hello world!
 "
             )
@@ -1606,8 +1606,8 @@ Hello world!
         assert_eq!(
             extract_messages(
                 "
-<!-- mdbook-xgettext-comment: this is a test -->
-<!-- mdbook-xgettext-comment: of a comment that spans. -->
+<!-- mdbook-xgettext:comment: this is a test -->
+<!-- mdbook-xgettext:comment: of a comment that spans. -->
 Greetings!
 "
             )
@@ -1630,11 +1630,11 @@ Greetings!
                 "
 before-no-comment
 
-<!-- mdbook-xgettext-comment: another -->
+<!-- mdbook-xgettext:comment: another -->
 Hello again, this is some text
 with a comment on it.
 
-<!-- mdbook-xgettext-comment: one more comment. -->
+<!-- mdbook-xgettext:comment: one more comment. -->
 after
 
 after-no-comment