improved raspbian detection

spells/menu/bitcoin/install-bitcoin

@@ -79,7 +79,7 @@ install_bitcoin() {
             ;;
         Linux)
             # If the operating system is Raspbian, we will skip compiling from source and go directly to binary installation.
-            if grep -q 'Raspbian' /etc/os-release; then
+            if uname -a | grep -q 'raspberrypi'; then
                 install_bitcoin_binary
             else
                 if ! install_bitcoin_from_source; then