Attempts to install fail because of "missing do in first path element"

Attempts at installing fail:

```
# git clone https://github.com/fullstorydev/grpcurl
Cloning into 'grpcurl'...
remote: Enumerating objects: 1028, done.
...
# cd grpcurl/
# make
go get -d -v -t ./...
go: downloading google.golang.org/protobuf v1.33.0
...
go: downloading golang.org/x/sync v0.5.0
ng github.com/kr/text v0.2.0
go: extracting github.com/rogpeppe/go-internal v1.9.0
github.com/fullstorydev/grpcurl imports
github.com/jhump/protoreflect/desc/protoparse imports
github.com/bufbuild/protocompile imports
io/fs: malformed module path "io/fs": missing dot in first path element
github.com/fullstorydev/grpcurl imports
github.com/golang/protobuf/proto imports
google.golang.org/protobuf/reflect/protodesc imports
google.golang.org/protobuf/internal/editiondefaults imports
embed: malformed module path "embed": missing dot in first path element
github.com/fullstorydev/grpcurl imports
google.golang.org/protobuf/types/known/structpb tested by
google.golang.org/protobuf/types/known/structpb.test imports
github.com/google/go-cmp/cmp/cmpopts tested by
github.com/google/go-cmp/cmp/cmpopts.test imports
net/netip: malformed module path "net/netip": missing dot in first path element
make: *** [Makefile:21: deps] Error 1

...
```

```
# go get github.com/fullstorydev/grpcurl/cmd/grpcurl
go: finding google.golang.org/grpc v1.57.1
...
go: finding cloud.google.com/go/compute/metadata v0.2.3
build github.com/fullstorydev/grpcurl/cmd/grpcurl: cannot load embed: malformed module path "embed": missing dot in first path element

```

Start by reproducing the reported `make` failure and the `go get github.com/fullstorydev/grpcurl/cmd/grpcurl` command. Inspect the dependency target at Makefile:21 and the cmd/grpcurl entry point, then determine the compatibility issue behind the malformed standard-library module paths. Done means the documented install commands complete successfully.

Written by the indexing model from the issue text.