Dynamic determine echo method depends on OS for sh

FreeBSD uses "echo" directly, the others use "/bin/echo"
Note that no matter which method we use, it won't work on Mac OS.

This commit fixed #4.

Author: PeterDaveHello

README.md

@@ -55,7 +55,7 @@ Make echo colorful with easier method. In [bash](https://www.gnu.org/software/ba
 
 * If you have [lolcat](https://github.com/busyloop/lolcat), you can also try `echo.Rainbow`.
 * If you are using Mac OS, please upgrade your bash first, you can use [Homebrew](http://brew.sh/) or [MacPorts](https://www.macports.org/), the origin bash is too old.
-* `ksh`/`sh` shell's color echo relys on external `/bin/echo`, it may not work properly with color under BSD and Mac OS.
+* `ksh`/`sh` shell's color echo may rely on external `/bin/echo`, it may not work properly with color under BSD and Mac OS.
 
 ## Screenshot
 

generator.sh

@@ -66,7 +66,7 @@ do
     "sh")
         fn=
         dot=
-        echo='/bin/echo'
+        echo='$ECHO'
         startSym='{'
         endSym='}'
         endIf='fi'
@@ -82,6 +82,15 @@ do
     fi
 
     echo "#!/usr/bin/env $shell" > "$newDist"
+    if [ "$shell" = "sh" ]; then
+        cat << SH_ECHO >> "$newDist"
+if [ "\`uname\`" = "FreeBSD" ]; then
+    ECHO="echo"
+else
+    ECHO="/bin/echo"
+fi
+SH_ECHO
+    fi
     for color in $(awk '{print $1}' "$table")
     do
         #light or not