allow ::AbstractString

Author: dehann

src/FileDFG/services/FileDFG.jl

@@ -17,7 +17,7 @@ v1 = addVariable!(dfg, :a, ContinuousScalar, labels = [:POSE], solvable=0)
 saveDFG(dfg, "/tmp/saveDFG.tar.gz")
 ```
 """
-function saveDFG( dfg::AbstractDFG, folder::String )
+function saveDFG( dfg::AbstractDFG, folder::AbstractString )
 
     # TODO: Deprecate the folder functionality in v0.6.1
 
@@ -82,7 +82,7 @@ loadDFG("/tmp/savedgraph.tar.gz", IncrementalInference, dfg)
 ls(dfg)
 ```
 """
-function loadDFG!(dfgLoadInto::AbstractDFG, dst::String)
+function loadDFG!(dfgLoadInto::AbstractDFG, dst::AbstractString)
 
 
     #