Don't ignore --color=never (#56)

Fixes a bug where `--color=never` was ignored.

src/app.rs

@@ -43,7 +43,7 @@ impl UseColor {
     match self {
       UseColor::Auto   => atty::is(stream),
       UseColor::Always => true,
-      UseColor::Never  => true,
+      UseColor::Never  => false,
     }
   }
 }

src/integration.rs

@@ -917,7 +917,7 @@ fn unknown_recipes() {
 }
 
 #[test]
-fn colors_with_context() {
+fn color_always() {
   integration_test(
     &["--color", "always"],
     "b = a\na = `exit 100`\nbar:\n echo '{{`exit 200`}}'",
@@ -927,6 +927,36 @@ fn colors_with_context() {
   );
 }
 
+#[test]
+fn color_never() {
+  integration_test(
+    &["--color", "never"],
+    "b = a\na = `exit 100`\nbar:\n echo '{{`exit 200`}}'",
+    100,
+    "",
+    "error: backtick failed with exit code 100
+  |
+2 | a = `exit 100`
+  |     ^^^^^^^^^^
+",
+  );
+}
+
+#[test]
+fn color_auto() {
+  integration_test(
+    &["--color", "auto"],
+    "b = a\na = `exit 100`\nbar:\n echo '{{`exit 200`}}'",
+    100,
+    "",
+    "error: backtick failed with exit code 100
+  |
+2 | a = `exit 100`
+  |     ^^^^^^^^^^
+",
+  );
+}
+
 #[test]
 fn colors_no_context() {
   let text ="