ci: remove minimal version check

It's impossible to do this without the cooperation of maintainers from
other core crates, and some of them do not see the value in doing this.

Author: BurntSushi

Diff for: ci/script.sh

@@ -49,7 +49,19 @@ if [ "$TRAVIS_RUST_VERSION" = "nightly" ]; then
   (cd bench && ./run rust --no-run --verbose)
 
   # Test minimal versions.
-  cargo +nightly generate-lockfile -Z minimal-versions
-  cargo build --verbose
-  cargo test --verbose
+  #
+  # For now, we remove this check, because it doesn't seem possible to convince
+  # some maintainers of *core* crates that this is a worthwhile test to add.
+  # In particular, this test uncovers any *incorrect* dependency specification
+  # in the chain of dependencies.
+  #
+  # We might consider figuring out how to migrate off of rand in order to get
+  # this check working. (This will be hard, since it either requires dropping
+  # quickcheck or migrating quickcheck off of rand, which is just probably
+  # not practical.)
+  #
+  # So frustrating.
+  # cargo +nightly generate-lockfile -Z minimal-versions
+  # cargo build --verbose
+  # cargo test --verbose
 fi