Update linux.md

installation/linux.md

@@ -115,7 +115,7 @@ Next, resynchronize the package index:
 sudo apt-get update
 ```
 
-##### Installing the latest version
+##### **Installing the latest version**
 
 Now install openHAB with the following command:
 
@@ -130,7 +130,7 @@ If you plan on disconnecting your machine from the internet, then you will want
 sudo apt-get install openhab-addons
 ```
 
-##### Prevent automatic upgrade of openHAB
+##### **Prevent automatic upgrade of openHAB**
 
 To prevent unexpected breakage by accidentally updating openHAB it's recommended to only manually upgrade to the newest version.
 This can be achieved by putting the openHAB package on "hold".
@@ -153,7 +153,7 @@ To show the packages on hold run
 sudo apt-mark showhold
 ```
 
-##### Installing a specific version
+##### **Installing a specific version**
 
 Installing a specific version is possible by specifing the version that should be installed.