app-vim/nvim-cmp: Replace 'echo' with ':;' in NOP

'echo' was abused to implement a no-operation (NOP) call in src_compile.
However that echo might have some implication like adding an empty line
into the compilation output. Dropping it in favor for ':;' instead which
is the usual style in other ebuilds.

Signed-off-by: Nils Freydank <nils.freydank@posteo.de>

app-vim/nvim-cmp/nvim-cmp-0.0.1.ebuild

@@ -40,7 +40,7 @@ DOCS=( README.md )
 
 src_compile(){
 	# Don't do anything. The Makefile runs only some linter for testing.
-	echo
+	:;
 }
 
 src_install(){