[Docs] Tweak some markup

Author: bbatsov

doc/modules/ROOT/pages/index.adoc

@@ -35,8 +35,8 @@ Projectile's features:
 * jump to a file in a directory
 * jump to a project buffer
 * jump to a test in project
-* toggle between files with same names but different extensions (e.g. `.h` \<-> `.c/.cpp`, `Gemfile` \<-> `Gemfile.lock`)
-* toggle between code and its test (e.g. `main.service.js` \<-> `main.service.spec.js`)
+* toggle between files with same names but different extensions (e.g. `.h` <--> `.c/.cpp`, `Gemfile` <--> `Gemfile.lock`)
+* toggle between code and its test (e.g. `main.service.js` <--> `main.service.spec.js`)
 * jump to recently visited files in the project
 * switch between projects you have worked on
 * kill all project buffers