Fix em-dash usage.

Author: Josh Rich

200_Language_intro/40_One_language_per_doc.asciidoc

@@ -2,8 +2,8 @@
 === One Language per Document
 
 A single predominant language per document requires a relatively simple setup.
-Documents from different languages can be stored in separate indices—`blogs-en`,
-`blogs-fr`, and so forth—that use the same fields for each index, just
+Documents from different languages can be stored in separate indices -- `blogs-en`,
+`blogs-fr`, and so forth -- that use the same fields for each index, just
 with different analyzers:
 
 [source,js]