json_normalize fails when input is a Series without a 0 in the index
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd
#construct a toy example
data = {0:{'id':1, 'name': 'Foo', 'elements': {'a':1}},1:{'id':2, 'name': 'Bar', 'elements': {'b':2}},2:{'id':3, 'name': 'Baz', 'elements': {'c':3}}}
passing_series = pd.Series(data)

#testing the passing case
pd.io.json.json_normalize(passing_series)
```
Output:
```python
Out[5]: 
   elements.a  elements.b  elements.c  id name
0         1.0         NaN         NaN   1  Foo
1         NaN         2.0         NaN   2  Bar
2         NaN         NaN         3.0   3  Baz
```
```python
#construct the failing case
failing_series = passing_series.copy()
failing_series.index = [1,2,3]

#testing the failing case
pd.io.json.json_normalize(failing_series)
```
Output:
```python
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-7-08797bc7d807> in <module>()
----> 1 pd.io.json.json_normalize(failing_series)

~/miniconda3/envs/uptodatepandas/lib/python3.5/site-packages/pandas/io/json/normalize.py in json_normalize(data, record_path, meta, meta_prefix, record_prefix, errors, sep)
    190 
    191     if record_path is None:
--> 192         if any([isinstance(x, dict) for x in compat.itervalues(data[0])]):
    193             # naive normalization, this is idempotent for flat records
    194             # and potentially will inflate the data considerably for

~/miniconda3/envs/uptodatepandas/lib/python3.5/site-packages/pandas/core/series.py in __getitem__(self, key)
    621         key = com._apply_if_callable(key, self)
    622         try:
--> 623             result = self.index.get_value(self, key)
    624 
    625             if not is_scalar(result):

~/miniconda3/envs/uptodatepandas/lib/python3.5/site-packages/pandas/core/indexes/base.py in get_value(self, series, key)
   2558         try:
   2559             return self._engine.get_value(s, k,
-> 2560                                           tz=getattr(series.dtype, 'tz', None))
   2561         except KeyError as e1:
   2562             if len(self) > 0 and self.inferred_type in ['integer', 'boolean']:

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_value()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_value()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.Int64HashTable.get_item()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.Int64HashTable.get_item()

KeyError: 0
```
#### Problem description

This is a bit of a stretch for this function, which calls for a dict or list of dicts, but generally `json_normalize` works just fine for Pandas Series. The exception, of course, being Series without a record whose index value is 0. The reason for this error is pretty obvious--line 192 of `pandas/io/json/normalize.py` attempts to get the first item from the passed `data` parameter with `[]` indexing. (i.e. `if any([isinstance(x, dict) for x in compat.itervalues(data[0])]):`)

#### Expected Output

Either an error for passing an invalid input type (not ideal), or just work correctly if passed a Series by checking the first record in a way that is compatible with Series as well as the standard (list). It seems like an improvement that would be pretty trivial to implement.

#### Output of ``pd.show_versions()``

<details>

[paste the output of ``pd.show_versions()`` here below this line]
pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.5.3.final.0
python-bits: 64
OS: Darwin
OS-release: 17.3.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.22.0
pytest: 3.2.1
pip: 9.0.1
setuptools: 36.4.0
Cython: 0.26
numpy: 1.13.1
scipy: 0.19.1
pyarrow: None
xarray: None
IPython: 6.1.0
sphinx: None
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.0.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.9999999
sqlalchemy: 1.1.5
pymysql: 0.7.9.None
psycopg2: 2.7.1 (dt dec pq3 ext lo64)
jinja2: 2.9.6
s3fs: 0.1.2
fastparquet: 0.1.0
pandas_gbq: None
pandas_datareader: None
</details>
