minor #13918 [travis] Do no tar in // (nicolas-grekas)

This PR was merged into the 2.3 branch.

Discussion
----------

[travis] Do no tar in //

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Using tar in parallel break 2.6 tests randomly with messages like "tar: Acl: file changed as we read it"
Removing parallel has no perf impact in this case and fixes the issue.
Best review with `?w=1`

Commits
-------

4f93aa3 [travis] Do no tar in //

Author: nicolas-grekas

.travis.sh

@@ -10,16 +10,15 @@ if [ -z "$components" ]; then
     exit 1
 fi
 echo '{"packages": {' > packages.json
-components=$(
-    for c in $components; do
-        sed -i ':a;N;$!ba;s#^{\n\(\s*\)\("name"\)#{\n\1"repositories": \[{ "type": "composer", "url": "file://'$(pwd)'/" }\],\n\1\2#' $c/composer.json
-        n=$(php -r '$n=json_decode(file_get_contents("'$c'/composer.json"));echo $n->name;')
-        echo '"'$n'": {"'$branch'.x-dev": ' >> packages.json
-        cat $c/composer.json >> packages.json
-        echo '"version": "'$branch.x-dev'",\n    "dist": {"type": "tar", "url": "file://'$(pwd)/$c'/package'$branch'.tar"}\n}},' >> packages.json
-        echo $c
-    done;
-)
+for c in $components; do
+    sed -i ':a;N;$!ba;s#^{\n\(\s*\)\("name"\)#{\n\1"repositories": \[{ "type": "composer", "url": "file://'$(pwd)'/" }\],\n\1\2#' $c/composer.json
+    n=$(php -r '$n=json_decode(file_get_contents("'$c'/composer.json"));echo $n->name;')
+    echo '"'$n'": {"'$branch'.x-dev": ' >> packages.json
+    cat $c/composer.json >> packages.json
+    echo '"version": "'$branch.x-dev'",\n    "dist": {"type": "tar", "url": "file://'$(pwd)/$c'/package'$branch'.tar"}\n}},' >> packages.json
+done;
 sed -i ':a;N;$!ba;s/\n}\n"/,\n    "/g' packages.json
 sed -i ':a;N;$!ba;s/}},$/\n}}\n}}/' packages.json
-echo "$components" | parallel --gnu "cd {}; tar -cf package$branch.tar --exclude='package*.tar' *"
+for c in $components; do
+    (cd $c && tar -cf package$branch.tar --exclude='package*.tar' *)
+done