Support long form of --verbose too.

Change-Id: I3fed750cad384374ae0e1d1bdde27fda468bf626
diff --git a/src/lib.rs b/src/lib.rs
index 977d730..7e5f11f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -291,7 +291,7 @@
         .version("v0.1.0")
         .setting(AppSettings::GlobalVersion)
         .about("Fargo is a prototype Fuchsia-specific wrapper around Cargo")
-        .arg(Arg::with_name("verbose").short("v").help(
+        .arg(Arg::with_name("verbose").long("verbose").short("v").help(
             "Print verbose output while performing commands",
         ))
         .arg(Arg::with_name("debug-os").long("debug-os").help(