lex: follow convention of colons at end of line

pages/common/lex.md

@@ -3,10 +3,10 @@
 > Lexical analyser generator.
 > Given a lexical analyser, generates C code implementing it.
 
-- Generate analyser from Lex file.
+- Generate analyser from Lex file:
 
 `lex {{path/to/example.l}}`
 
-- Compile a C file generated by lex.
+- Compile a C file generated by lex:
 
 `cc {{path/to/lex.yy.c}} -o {{example}}`