add iconv in alpine

Dockerfile.alpine

@@ -9,18 +9,17 @@ RUN apk add --quiet --no-cache \
     apache2 \
     wget \
     curl \
-    && apk add --quiet --no-cache --virtual .build-deps \
-        build-base \
-        autoconf \
-        libpng-dev \
-        libjpeg-turbo-dev \
-        libwebp-dev \
-        freetype-dev \
-        libxml2-dev \
-        mariadb-connector-c-dev \
-        postgresql-dev \
-        sqlite-dev \
-    && install-php-extensions gd pdo pdo_mysql pdo_pgsql pdo_sqlite pgsql zip \
+    build-base \
+    autoconf \
+    libpng-dev \
+    libjpeg-turbo-dev \
+    libwebp-dev \
+    freetype-dev \
+    libxml2-dev \
+    mariadb-connector-c-dev \
+    postgresql-dev \
+    sqlite-dev \
+    && install-php-extensions iconv gd pdo pdo_mysql pdo_pgsql pdo_sqlite pgsql zip \
     && apk del .build-deps
 
 # Note: PHP extensions are provided via Alpine `php-*` packages above.