Cargo.toml: update dependencies

Update dependencies as long as it does not break the lib. In fact, there
is just one dependency that cannot be updated to its latest version:
"combine", currently at 3.6.0, with major API changes between v2 and v3.
Let's stick to v2 for now.

Thanks to @jackcmay for this update.

Fixes #35.

Cargo.toml

@@ -24,12 +24,12 @@ include = [
 
 [dependencies]
 
-combine = "2.1.1"
-libc = "0.2.0"
+combine = "2.5"
+libc = "0.2"
 time = "0.1"
-byteorder = "1.2.1"
+byteorder = "1.2"
 
 [dev-dependencies]
 
 elf = "0.0.10"
-json = "0.11.4"
+json = "0.11"