fix the link to the script in the doc. fix some error messages (#960)

Author: shahasad

docs/ContribOperators.md

@@ -1,6 +1,6 @@
 ## Contrib Operator Schemas
 *This file is automatically generated from the
-            [def files](/onnxruntime/core/graph/contrib_ops/contrib_defs.cc) via [this script](/onnxruntime/python/tools/gen_doc.py).
+            [def files](/onnxruntime/core/graph/contrib_ops/contrib_defs.cc) via [this script](/tools/python/gen_doc.py).
             Do not modify directly and instead edit operator definitions.*
 
 * com.microsoft

tools/ci_build/build.py

@@ -658,7 +658,7 @@ def generate_documentation(source_dir, build_dir, configs):
 
 
     if len(docdiff) > 0:
-        raise BuildError("The updated operator document file "+operator_doc_path+" must be checked in.\n diff:\n"+docdiff)
+        raise BuildError('The updated operator document file '+str(operator_doc_path)+' must be checked in.\n diff:\n'+str(docdiff))
 
 
 def main():

tools/python/gen_doc.py

@@ -307,7 +307,7 @@ def main(args):  # type: (Type[Args]) -> None
         fout.write('## Contrib Operator Schemas\n')
         fout.write(
             "*This file is automatically generated from the\n"
-            "            [def files](/onnxruntime/core/graph/contrib_ops/contrib_defs.cc) via [this script](/onnxruntime/python/tools/gen_doc.py).\n"
+            "            [def files](/onnxruntime/core/graph/contrib_ops/contrib_defs.cc) via [this script](/tools/python/gen_doc.py).\n"
             "            Do not modify directly and instead edit operator definitions.*\n")
 
         # domain -> support level -> name -> [schema]