Merge pull request #68 from bluss/impl-warning

Impl warning
diff --git a/.travis.yml b/.travis.yml
index 9fb0b09..9582b44 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,6 +2,7 @@
 sudo: false
 matrix:
   include:
+    - rust: 1.6.0
     - rust: stable
     - rust: stable
       env:
diff --git a/Cargo.toml b/Cargo.toml
index d62df44..48d08d5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 
 name = "petgraph"
-version = "0.2.5"
+version = "0.2.6"
 license = "MIT/Apache-2.0"
 authors = [
 "bluss",
diff --git a/README.rst b/README.rst
index d020b27..a841c52 100644
--- a/README.rst
+++ b/README.rst
@@ -19,6 +19,10 @@
 Recent Changes
 --------------
 
+- 0.2.6
+
+  - Fix warning about type parameter defaults (no functional change)
+
 - 0.2.5
 
   - Add SubTopo, a topo walker for the subgraph reachable from a starting point.
diff --git a/src/graph.rs b/src/graph.rs
index 4fbc0cb..675b74b 100644
--- a/src/graph.rs
+++ b/src/graph.rs
@@ -71,7 +71,7 @@
 #[derive(Copy, Clone, Debug, PartialEq, PartialOrd, Eq, Ord, Hash)]
 pub struct NodeIndex<Ix=DefIndex>(Ix);
 
-impl<Ix: IndexType = DefIndex> NodeIndex<Ix>
+impl<Ix: IndexType> NodeIndex<Ix>
 {
     #[inline]
     pub fn new(x: usize) -> Self {
@@ -109,7 +109,7 @@
 #[derive(Copy, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
 pub struct EdgeIndex<Ix=DefIndex>(Ix);
 
-impl<Ix: IndexType = DefIndex> EdgeIndex<Ix>
+impl<Ix: IndexType> EdgeIndex<Ix>
 {
     #[inline]
     pub fn new(x: usize) -> Self {
@@ -158,7 +158,7 @@
     next: [EdgeIndex<Ix>; 2],
 }
 
-impl<N, Ix: IndexType = DefIndex> Node<N, Ix>
+impl<N, Ix: IndexType> Node<N, Ix>
 {
     /// Accessor for data structure internals: the first edge in the given direction.
     pub fn next_edge(&self, dir: EdgeDirection) -> EdgeIndex<Ix>
@@ -178,7 +178,7 @@
     node: [NodeIndex<Ix>; 2],
 }
 
-impl<E, Ix: IndexType = DefIndex> Edge<E, Ix>
+impl<E, Ix: IndexType> Edge<E, Ix>
 {
     /// Accessor for data structure internals: the next edge for the given direction.
     pub fn next_edge(&self, dir: EdgeDirection) -> EdgeIndex<Ix>