Make indexmap required dep
diff --git a/Cargo.toml b/Cargo.toml
index df77606..c5f91a6 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -30,7 +30,7 @@
[dependencies]
fixedbitset = { version = "0.2.0", default-features = false }
quickcheck = { optional = true, version = "0.8", default-features = false }
-indexmap = { version = "1.0.2", optional = true }
+indexmap = { version = "1.0.2" }
serde = { version = "1.0", optional = true }
serde_derive = { version = "1.0", optional = true }
@@ -42,7 +42,7 @@
[features]
default = ["graphmap", "stable_graph", "matrix_graph"]
-graphmap = ["indexmap"]
+graphmap = []
serde-1 = ["serde", "serde_derive"]
stable_graph = []
matrix_graph = []