Update scala/app snippet to extend App
Update scala/app snippet to extend App

Earlier versions of Scala let its users extend a trait `Application` to
avoid boilerplate when writing a main program. The `Application` trait
was deprecated in Scala 2.9, and replaced by the `App` trait
(`Application` was subsequently removed in Scala 2.11). This commit
replaces `Application` with `App` in the `app` snippet.

bixuanzju/yasnippet-snippets,Emacs-Phoenix/yasnippet-snippets,s9gf4ult/yasnippet-snippets,s9gf4ult/yasnippet-snippets,nofxx/yasnippet-snippets,gbalats/yasnippet-snippets,cook/yasnippet-snippets,lmouelle/yasnippet-snippets,zhuoyikang/yasnippet-snippets,jordonbiondo/yasnippet-snippets,gfanton/yasnippet-snippets,octopuscabbage/yasnippet-snippets,lmouelle/yasnippet-snippets,jacobono/yasnippet-snippets,jferguson-gnubio/yasnippet-snippets,ageekymonk/yasnippet-snippets,nofxx/yasnippet-snippets,cook/yasnippet-snippets,bo0ts/yasnippet-snippets,jlhg/yasnippet-snippets,s9gf4ult/yasnippet-snippets,lmouelle/yasnippet-snippets,shafayetkhan/yasnippet-snippets,bixuanzju/yasnippet-snippets,npe9/yasnippet-snippets,cook/yasnippet-snippets,zhuoyikang/yasnippet-snippets,gfanton/yasnippet-snippets,bixuanzju/yasnippet-snippets,npe9/yasnippet-snippets,gbalats/yasnippet-snippets,npe9/yasnippet-snippets,Emacs-Phoenix/yasnippet-snippets,Emacs-Phoenix/yasnippet-snippets,bo0ts/yasnippet-snippets,octopuscabbage/yasnippet-snippets,jferguson-gnubio/yasnippet-snippets,jferguson-gnubio/yasnippet-snippets,shafayetkhan/yasnippet-snippets,ageekymonk/yasnippet-snippets,jordonbiondo/yasnippet-snippets,jacobono/yasnippet-snippets,gbalats/yasnippet-snippets,gfanton/yasnippet-snippets,nofxx/yasnippet-snippets,jordonbiondo/yasnippet-snippets,bo0ts/yasnippet-snippets,octopuscabbage/yasnippet-snippets,ageekymonk/yasnippet-snippets,zhuoyikang/yasnippet-snippets,jacobono/yasnippet-snippets,shafayetkhan/yasnippet-snippets