Error in join: expected string for sequence element 0, got 'path'

While trying to build an iOS application linked to some pods (non-vendored), I get the following error:
```
(16:37:49) INFO: Invocation ID: e462672e-427c-4928-8d68-e4763ee2d6ad
(16:37:53) INFO: Repository Logging instantiated at:
/Volumes/VANTAGE/platform/WORKSPACE:307:19: in
/private/var/tmp/_bazel_sam.g/.../external/rules_pods/BazelExtensions/workspace.bzl:275:14: in new_pod_repository
Repository rule pod_repo_ defined at:
/private/var/tmp/_bazel_sam.g/.../external/rules_pods/BazelExtensions/workspace.bzl:173:28: in
(16:37:53) ERROR: An error occurred during the fetch of repository 'Logging':
Traceback (most recent call last):
File "/private/var/tmp/_bazel_sam.g/.../external/rules_pods/BazelExtensions/workspace.bzl", line 105, column 27, in _impl
_fetch_remote_repo(
File "/private/var/tmp/_bazel_sam.g/.../external/rules_pods/BazelExtensions/workspace.bzl", line 47, column 25, in _fetch_remote_repo
fetch_output = _exec(repository_ctx, fetch_cmd)
File "/private/var/tmp/_bazel_sam.g/.../external/rules_pods/BazelExtensions/workspace.bzl", line 7, column 50, in _exec
fail("Could not exec command " + " ".join(command))
Error in join: expected string for sequence element 0, got 'path'
(16:37:53) ERROR: Error fetching repository: Traceback (most recent call last):
File "/private/var/tmp/_bazel_sam.g/.../external/rules_pods/BazelExtensions/workspace.bzl", line 105, column 27, in _impl
_fetch_remote_repo(
File "/private/var/tmp/_bazel_sam.g/.../external/rules_pods/BazelExtensions/workspace.bzl", line 47, column 25, in _fetch_remote_repo
fetch_output = _exec(repository_ctx, fetch_cmd)
File "/private/var/tmp/_bazel_sam.g/.../external/rules_pods/BazelExtensions/workspace.bzl", line 7, column 50, in _exec
fail("Could not exec command " + " ".join(command))
Error in join: expected string for sequence element 0, got 'path'
```

I figured this might be an incompatibility with Bazel 4.0.0, which we recently switched to. I saw the recent commits on `master` related to Bazel 4 compatibility, but when using `master` directly, I run into #112.

**`WORKSPACE`**:
```starlark
http_archive(
name = "rules_pods",
urls = ["https://github.com/pinterest/PodToBUILD/releases/download/0.25.2-8a5efa0/PodToBUILD.zip"],
sha256 = "db4256e80fda350bff752f70385f3a332ac8b93d63c3ef677b11dca075dbe1ff",
)
load("@rules_pods//BazelExtensions:workspace.bzl", "new_pod_repository")

new_pod_repository(
name = "Logging",
url = "https://github.com/apple/swift-log/archive/173f567a2dfec11d74588eea82cecea555bdc0bc.zip",
podspec_url = "https://raw.githubusercontent.com/CocoaPods/Specs/master/Specs/8/d/b/Logging/1.2.0/Logging.podspec.json",
generate_module_map = False,
inhibit_warnings = True,
)
```