Allow latter --web-bundle to override the former

This makes use of `Arg::overrides_with` since clap v2.29.3.

Author: bryango

src/bin/tectonic/compile.rs

@@ -37,7 +37,7 @@ pub struct CompileOptions {
     bundle: Option<PathBuf>,
 
     /// Use this URL to find resource files instead of the default
-    #[structopt(takes_value(true), long, short, name = "url")]
+    #[structopt(takes_value(true), long, short, name = "url", overrides_with = "url")]
     // TODO add URL validation
     web_bundle: Option<String>,
 

src/bin/tectonic/v2cli.rs

@@ -678,7 +678,7 @@ pub struct NewCommand {
     path: PathBuf,
 
     /// Use this URL to find resource files instead of the default
-    #[structopt(takes_value(true), long, short, name = "url")]
+    #[structopt(takes_value(true), long, short, name = "url", overrides_with = "url")]
     // TODO add URL validation
     web_bundle: Option<String>,
 }
@@ -709,7 +709,7 @@ impl NewCommand {
 #[derive(Debug, Eq, PartialEq, StructOpt)]
 pub struct InitCommand {
     /// Use this URL to find resource files instead of the default
-    #[structopt(takes_value(true), long, short, name = "url")]
+    #[structopt(takes_value(true), long, short, name = "url", overrides_with = "url")]
     // TODO add URL validation
     web_bundle: Option<String>,
 }