binman: Switch to 'python-coverage'

The most portable way to get access to coverage is to invoke it as
'python-coverage'.

Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/README b/tools/binman/README
index 22f21bc..f74e392 100644
--- a/tools/binman/README
+++ b/tools/binman/README
@@ -583,8 +583,7 @@
 
 To enable Python test coverage on Debian-type distributions (e.g. Ubuntu):
 
-   $ sudo apt-get install python-pip python-pytest
-   $ sudo pip install coverage
+   $ sudo apt-get install python-coverage python-pytest
 
 
 Advanced Features / Technical docs