Fix Commonmark rendering on Github

Replace NBSP with SPACE.

README.md

@@ -17,7 +17,7 @@ need of logging the Zonemaster test runs in one's own respective database for
 analysing.  
 
 
-### Prerequisites
+### Prerequisites
 
 Before you install the Zonemaster Backend, you need the
 Zonemaster Engine installed. Please see the
@@ -46,7 +46,7 @@ Zonemaster *Backend* is configured as a whole from `/etc/zonemaster/backend_conf
 >
 
 
-### Documentation
+### Documentation
 
 The Zonemaster Backend documentation is split up into several documents:
 

docs/installation.md

@@ -209,7 +209,7 @@ The command is expected to give an immediate JSON response similiar to :
 {"id":140715758026879,"jsonrpc":"2.0","result":"Zonemaster Test Engine Version: v1.0.2"}
 ```
 
-## <a name="debian"></a>2. Ubuntu & Debian 
+## <a name="debian"></a>2. Ubuntu & Debian 
 
 ### 2.1 Installing dependencies