checksums: use sha256 checksums everywhere

We'd like to use a consistent checksum scheme everywhere so that we can:

    a) incorporate archive checksums into our specs and have a
       consistent hashing algorithm across all specs.

    b) index mirrors with a consistent type of checksum, and not one that
       is dependent on how spack packages are written.

- [x] convert existing md5, sha224, sha512, sha1 checksums to sha256

var/spack/repos/builtin/packages/r-cubature/package.py

@@ -15,6 +15,6 @@ class RCubature(RPackage):
 
     version('2.0.3', sha256='79bf03ebdb64b0de1ef19d24051b9d922df9310254bee459bb47764522407a73')
     version('2.0.2', sha256='641165c665ff490c523bccc05c42bb6851e42676b6b366b55fc442a51a8fbe8c')
-    version('1.1-2', '5617e1d82baa803a3814d92461da45c9')
+    version('1.1-2', sha256='0a05469bdc85d6bd8165a42a3fc5c35a06700d279e4e8b3cf4669df19edffeed')
 
     depends_on('r-rcpp', when='@2.0.3:', type=('build', 'run'))