Update string_color.md

Change the text "Rocky" to "world" to match the screenshot correctly

Author: jimcat8

docs/gemstones/string_color.md

@@ -66,23 +66,23 @@ We can write a script to observe the color change.
 # Font color cycle
 for color1 in {31..37}
     do
-        echo -e "\033[0;${color1};40m---hello! Rocky---\033[0m"
+        echo -e "\033[0;${color1};40m---hello! world---\033[0m"
     done
 
 echo "-------"
 
 # Background color cycle
 for color2 in {40..47}
     do
-        echo -e "\033[30;${color2}m---hello! Rocky---\033[0m"
+        echo -e "\033[30;${color2}m---hello! world---\033[0m"
     done
 
 echo "-------"
 
 # Cycle of display mode
 for color3 in 0 1 4 5 7 8
     do
-        echo -e "\033[${color3};37;40m---hello! Rocky---\033[0m"
+        echo -e "\033[${color3};37;40m---hello! world---\033[0m"
     done
 ```