code style: fixed slice initialization in mite package

A nil slice is for the purpose of append a slice even though it points
to nothing. See: https://blog.golang.org/slices

mite/project.go

@@ -27,13 +27,13 @@ func (r *projectResponse) ToProject() *Project {
 }
 
 func (a *miteApi) Projects() ([]*Project, error) {
-	prs := []projectResponse{}
+	var prs []projectResponse
 	err := a.get("projects.json", &prs)
 	if err != nil {
 		return nil, err
 	}
 
-	projects := []*Project{}
+	var projects []*Project
 	for _, pr := range prs {
 		projects = append(projects, pr.ToProject())
 	}

mite/service.go

@@ -27,13 +27,13 @@ func (r *serviceResponse) ToService() *Service {
 }
 
 func (a *miteApi) Services() ([]*Service, error) {
-	srs := []serviceResponse{}
+	var srs []serviceResponse
 	err := a.get("services.json", &srs)
 	if err != nil {
 		return nil, err
 	}
 
-	services := []*Service{}
+	var services []*Service
 	for _, sr := range srs {
 		services = append(services, sr.ToService())
 	}

mite/time_entry.go

@@ -113,13 +113,13 @@ func (r *timeEntryResponse) ToTimeEntry() *TimeEntry {
 }
 
 func (a *miteApi) TimeEntries(query *TimeEntryQuery) ([]*TimeEntry, error) {
-	ter := []timeEntryResponse{}
+	var ter []timeEntryResponse
 	err := a.getParametrized("time_entries.json", query.toValues(), &ter)
 	if err != nil {
 		return nil, err
 	}
 
-	timeEntries := []*TimeEntry{}
+	var timeEntries []*TimeEntry
 	for _, te := range ter {
 		timeEntries = append(timeEntries, te.ToTimeEntry())
 	}