Fix custom steps in Windows (fix #205)

src/steps/generic.rs

@@ -1,6 +1,6 @@
 use crate::error::{Error, ErrorKind};
 use crate::executor::{CommandExt, RunType};
-use crate::terminal::print_separator;
+use crate::terminal::{print_separator, shell};
 use crate::utils::{self, PathExt};
 use directories::BaseDirs;
 use failure::ResultExt;
@@ -110,7 +110,7 @@ pub fn run_myrepos_update(base_dirs: &BaseDirs, run_type: RunType) -> Result<(),
 
 pub fn run_custom_command(name: &str, command: &str, run_type: RunType) -> Result<(), Error> {
     print_separator(name);
-    run_type.execute("sh").arg("-c").arg(command).check_run()
+    run_type.execute(shell()).arg("-c").arg(command).check_run()
 }
 
 pub fn run_composer_update(base_dirs: &BaseDirs, run_type: RunType) -> Result<(), Error> {

src/terminal.rs

@@ -23,12 +23,12 @@ lazy_static! {
 }
 
 #[cfg(unix)]
-fn shell() -> String {
+pub fn shell() -> String {
     env::var("SHELL").unwrap_or_else(|_| "sh".to_string())
 }
 
 #[cfg(windows)]
-fn shell() -> &'static str {
+pub fn shell() -> &'static str {
     which("pwsh").map(|_| "pwsh").unwrap_or("powershell")
 }