Try to fix Travis build

.travis.yml

@@ -7,6 +7,7 @@ matrix:
     - rust: 1.24.0
       script:
         # Build only the library (examples may fail)
+        - cargo update
         - cargo update -p cfg-if --precise 0.1.9
         - cargo update -p log --precise 0.4.8
         - cargo build --verbose
@@ -18,6 +19,7 @@ matrix:
         # nostd build
         # byteorder crate version is configured here to fix build in old nightly compiler
         # See: https://github.com/BurntSushi/byteorder/pull/150
+        - cargo update
         - cargo update -p byteorder --precise 1.2.7
         - cargo update -p cfg-if --precise 0.1.9
         - cargo update -p log --precise 0.4.8