fix: gh-r retrieves release data GH REST API (zdharma-continuum#373)

Recent changes to GitHub HTML structure broke `gh-r` & `bpick` ices method of parsing project release assets.

- `gh-r` utilizes official GitHub REST API to retrieve project releases data
- add `local` scope to `releases_url` variable

# closes zdharma-continuum#374 

Co-authored-by: Tyler Wardhaugh <tyler.wardhaugh@gmail.com>

zinit-install.zsh

@@ -354,7 +354,13 @@ builtin source "${ZINIT[BIN_DIR]}/zinit-side.zsh" || {
 
     (
         if [[ $site = */releases ]] {
-            local url=$site/${ICE[ver]}
+            local tag_version=${ICE[ver]}
+            if [[ -z $tag_version ]]; then
+                tag_version="$( { .zinit-download-file-stdout $site/latest || .zinit-download-file-stdout $site/latest 1; } 2>/dev/null | \
+                                  command grep -m1 -o 'href=./'$user'/'$plugin'/releases/tag/[^"]\+')"
+                tag_version=${tag_version##*/}
+            fi
+            local url=$site/expanded_assets/$tag_version
 
             .zinit-get-latest-gh-r-url-part "$user" "$plugin" "$url" || return $?
 
@@ -1456,7 +1462,14 @@ builtin source "${ZINIT[BIN_DIR]}/zinit-side.zsh" || {
     local user=$1 plugin=$2 urlpart=$3
 
     if [[ -z $urlpart ]] {
-        local url=https://github.com/$user/$plugin/releases/$ICE[ver]
+        local tag_version=${ICE[ver]}
+        if [[ -z $tag_version ]]; then
+            local releases_url=https://github.com/$user/$plugin/releases/latest
+            tag_version="$( { .zinit-download-file-stdout $releases_url || .zinit-download-file-stdout $releases_url 1; } 2>/dev/null | \
+                              command grep -m1 -o 'href=./'$user'/'$plugin'/releases/tag/[^"]\+')"
+            tag_version=${tag_version##*/}
+        fi
+        local url=https://github.com/$user/$plugin/releases/expanded_assets/$tag_version
     } else {
         local url=https://$urlpart
     }