Don't choke on SSH Git URLs.

lib/src/source/git.dart

Index: lib/src/source/git.dart
diff --git a/lib/src/source/git.dart b/lib/src/source/git.dart
index 06981fab70f821a28b3836f5956bd46a29c45f58..8fc1014606c7ed274a503983b859b7fb83dce696 100644
--- a/lib/src/source/git.dart
+++ b/lib/src/source/git.dart
@@ -135,8 +135,7 @@ class GitSource extends CachedSource {
           "string.");
     }
 
-    // Ensure that it's a valid URL.
-    Uri.parse(description["url"]);
+    _validateUrl(description["url"]);
 
     var ref = description["ref"];
     if (ref != null && ref is! String) {
@@ -161,8 +160,7 @@ class GitSource extends CachedSource {
           "string.");
     }
 
-    // Ensure that it's a valid URL.
-    Uri.parse(description["url"]);
+    _validateUrl(description["url"]);
 
     var ref = description["ref"];
     if (ref != null && ref is! String) {
@@ -182,6 +180,16 @@ class GitSource extends CachedSource {
     });
   }
 
+  /// Throws a [FormatException] if [url] isn't a valid Git URL.
+  void _validateUrl(String url) {
+    // If the URL contains an @, it's probably an SSH hostname, which we don't
+    // know how to validate.
+    if (url.contains("@")) return;
+
+    // Otherwise, we use Dart's URL parser to validate the URL.
+    Uri.parse(url);
+  }
+
   /// If [description] has a resolved ref, print it out in short-form.
   ///
   /// This helps distinguish different git commits with the same pubspec