Add testing of minimal versions

Closes rust-random#741

This seems to require a couple of hacks unfortunately.

.travis.yml

@@ -66,6 +66,13 @@ matrix:
       env: DESCRIPTION="Miri, nightly"
       script:
         - sh utils/ci/miri.sh
+
+    - rust: nightly
+      os: linux
+      env: DESCRIPTION="Minimal dep versions"
+      script:
+        - cargo generate-lockfile -Z minimal-versions
+        - bash utils/ci/script.sh
 
 before_install:
   - set -e

rand_distr/Cargo.toml

@@ -24,4 +24,6 @@ rand = { path = "..", version = "0.7" }
 [dev-dependencies]
 rand_pcg = { version = "0.2", path = "../rand_pcg" }
 # Histogram implementation for testing uniformity
-average = "0.9.2"
+average = "0.10.0"
+# Not a direct dependency but required to boost the minimum version:
+conv = "0.3.2"

rand_isaac/Cargo.toml

@@ -23,9 +23,11 @@ serde1 = ["serde", "rand_core/serde1"]
 
 [dependencies]
 rand_core = { path = "../rand_core", version = "0.5" }
-serde = { version = "1", features = ["derive"], optional = true }
+serde = { version = "1.0.63", features = ["derive"], optional = true }
+# Not a direct dependency but required to boost the minimum version:
+serde_derive = { version = "1.0.63", optional = true }
 
 [dev-dependencies]
 # This is for testing serde, unfortunately we can't specify feature-gated dev
 # deps yet, see: https://github.com/rust-lang/cargo/issues/1596
-bincode = "1"
+bincode = "1.1.4"