Fix oh-my-fish (#524)

src/steps/os/unix.rs

@@ -31,10 +31,15 @@ pub fn run_fisher(base_dirs: &BaseDirs, run_type: RunType) -> Result<()> {
 }
 
 pub fn run_oh_my_fish(ctx: &ExecutionContext) -> Result<()> {
-    let omf = require("omf")?;
+    let fish = require("fish")?;
+    ctx.base_dirs()
+        .home_dir()
+        .join(".local/share/omf/pkg/omf/functions/omf.fish")
+        .require()?;
 
     print_separator("oh-my-fish");
-    ctx.run_type().execute(&omf).arg("update").check_run()
+
+    ctx.run_type().execute(&fish).args(&["-c", "omf update"]).check_run()
 }
 
 pub fn run_brew(ctx: &ExecutionContext) -> Result<()> {