Replace dash with underscore in target name

Dash is not allowed in crate names and replaced with underscore.

This is trying to fix #15.

Author: onur

src/db/add_package.rs

@@ -54,7 +54,7 @@ pub fn add_package_into_database(conn: &Connection,
                                          &format!("{}", pkg.manifest().version()),
                                          &release_time,
                                          &dependencies.to_json(),
-                                         &pkg.targets()[0].name(),
+                                         &pkg.targets()[0].name().replace("-", "_"),
                                          &yanked,
                                          &res.build_success,
                                          &res.have_doc,

src/docbuilder/chroot_builder.rs

@@ -277,7 +277,7 @@ impl DocBuilder {
             .join(&self.options.chroot_user)
             .join(canonical_name(&package))
             .join("doc")
-            .join(package.targets()[0].name().to_string());
+            .join(package.targets()[0].name().replace("-", "_").to_string());
         crate_doc_path.exists()
     }