docs: update abs.md

Author: boriel

docs/abs.md

@@ -3,20 +3,20 @@
 ## Syntax
 
 
-```
+```basic
 ABS(numericExpression)
 ```
 
 
 ## Description
 
 Returns the absolute value of the given argument.
-Argument must be a numeric expression. Returned value has the same type as the input argument.
+Argument must be a numeric expression. The returned value has the same type as the input argument.
 
 ## Examples
 
 
-```
+```basic
 REM Absolute value
 LET a = -1
 PRINT "Absolute value of a is "; ABS(a)