Update Cargo manifest

- use recommended form for license descriptor
- remove travis CI badge, as Travis is no longer used for CI

Cargo.toml

@@ -5,7 +5,7 @@ description = "Rust implementation of the NIfTI file format"
 documentation = "https://docs.rs/crate/nifti"
 edition = "2018"
 keywords = ["nifti", "neuroimaging", "standard", "parser"]
-license = "MIT/Apache-2.0"
+license = "MIT OR Apache-2.0"
 name = "nifti"
 readme = "README.md"
 repository = "https://github.com/Enet4/nifti-rs"
@@ -17,10 +17,6 @@ features = ["ndarray_volumes", "nalgebra_affine"]
 
 [badges]
 
-[badges.travis-ci]
-branch = "master"
-repository = "Enet4/nifti-rs"
-
 [dependencies]
 approx = "0.4"
 byteordered = "0.5"