ci: Separate caches + don't use local nix

.gitlab-ci.yml

@@ -5,12 +5,11 @@ variables:
 before_script:
   - apt-get update -qq
   - apt-get install -qq build-essential curl git
-cache:
-  paths:
-    - cargo/
-    - target/
-
 format:
+  cache:
+    paths:
+      - cargo/
+      - target/
   script:
     - rustup default nightly
     - rustup component add rustfmt
@@ -18,11 +17,19 @@ format:
 
 linux:
   image: 'rust:1.35.0'
+  cache:
+    paths:
+      - cargo/
+      - target/
   script:
     - cargo check
     - FULL=1 make tests
 
 linux:stable:
+  cache:
+    paths:
+      - cargo/
+      - target/
   script:
     - cargo check
     - TOOLCHAIN= make tests

Cargo.toml

@@ -88,7 +88,7 @@ structopt = "^0.2"
 atty = "0.2"
 permutate = "0.3"
 xdg = "2.1"
-nix = { path = "../nix" }
+nix = "0.14"
 
 [target."cfg(all(unix, not(target_os = \"redox\")))".dependencies]
 users = "0.9"