Get rid of lsb-release dependency (#16)

У всех линуксов уже давно есть /etc/os-release, и можно на него опираться, упрощая жизнь и уменьшая количество зависимостей для конфига.

Reviewed-on: #16
Reviewed-by: Stanislav Nikitin <pztrn@pztrn.name>
Co-authored-by: Vladimir Hodakov <vladimir@hodakov.me>
Co-committed-by: Vladimir Hodakov <vladimir@hodakov.me>

zsh/03-vars.zsh

@@ -6,9 +6,9 @@ OS_RELEASE=`uname -r`
 OS_ARCH=`uname -m`
 
 # Distro detection.
-LSBRELEASE=$(which lsb_release)
-if [ $? -eq 0 ]; then
-  DISTRO=`lsb_release -i -s`
+if [[ -f /etc/os-release ]]; then
+  . /etc/os-release
+  DISTRO=${ID}
 else
   # BSDs OS and macOS can be detected via uname.
   DISTRO=${OS}