update num-derive to 0.3 change minimal rustc to 1.34.2

.travis.yml

@@ -1,6 +1,6 @@
 language: rust
 rust:
-    - 1.24.1
+    - 1.34.2
     - stable
     - beta
     - nightly

Cargo.toml

@@ -19,7 +19,7 @@ exclude = ["tests/images/*", "tests/fuzz_images/*"]
 [dependencies]
 byteorder = "1.2"
 lzw = "0.10"
-num-derive = "0.2"
+num-derive = "0.3"
 num-traits = "0.2"
 
 [dev-dependencies]