Improve shell detection code

using `ps` to detect the shell fails in some cases (For me, it is using
a docker container to run an x86 OS image on an M1 Mac - the process is
is /usr/bin/qemu-x86_64 /bin/bash)

Using the $[SHELL]-VERSION environment variables is probably the most
fool-proof way to detect the shell.

libexec/jenv-init

@@ -22,13 +22,13 @@ done
 
 shell="$1"
 if [ -z "$shell" ]; then
-  if [-n "$BASH_VERSIONH"]; then
+  if [ -n "$BASH_VERSION" ]; then
       shell="bash"
-  elif [ -n "$ZSH_VERSION"]; then
+  elif [ -n "$ZSH_VERSION" ]; then
       shell="zsh"
-  elif [ -n "FISH_VERSION"]; then
+  elif [ -n "$FISH_VERSION" ]; then
       shell="fish"
-  elif [ -n "KSH_VERSION"]; then
+  elif [ -n "$KSH_VERSION" ]; then
       shell="ksh"
   else
       shell="unknown"