Add an option to ignore build dependencies

this fixes sfackler#51

src/args.rs

@@ -39,6 +39,9 @@ pub struct Args {
     #[structopt(long = "no-dev-dependencies")]
     /// Skip dev dependencies.
     pub no_dev_dependencies: bool,
+    #[structopt(long = "no-build-dependencies")]
+    /// Skip build dependencies.
+    pub no_build_dependencies: bool,
     #[structopt(long = "manifest-path", value_name = "PATH", parse(from_os_str))]
     /// Path to Cargo.toml
     pub manifest_path: Option<PathBuf>,

src/graph.rs

@@ -51,6 +51,9 @@ pub fn build(args: &Args, metadata: Metadata) -> Result<Graph, Error> {
                 if args.no_dev_dependencies && kind == DependencyKind::Development {
                     continue;
                 }
+                if args.no_build_dependencies && kind == DependencyKind::Build {
+                    continue;
+                }
 
                 graph.graph.add_edge(from, to, kind);
             }