Fix string formatting

bilby/gw/detector/__init__.py

@@ -235,9 +235,9 @@ def load_data_from_cache_file(
     with open(cache_file, 'r') as ff:
         lines = ff.readlines()
         if len(lines)>1:
-            raise ValueError('This method cannot handle cache files with
-                              multiple frames. Use `load_data_by_channel_name
-                              instead.')
+            raise ValueError('This method cannot handle cache files with'
+                             ' multiple frames. Use `load_data_by_channel_name'
+                             ' instead.')
         else:
             line = lines[0]
             cache = lal.utils.cache.CacheEntry(line)
@@ -250,11 +250,11 @@ def load_data_from_cache_file(
             ifo = get_empty_interferometer(
                 "{}1".format(cache.observatory))
             if not data_in_cache:
-                raise ValueError('The specified data segment does not exist in
-                                  this frame.')
+                raise ValueError('The specified data segment does not exist in' 
+                                 ' this frame.')
             if not psd_in_cache:
-                raise ValueError('The specified PSD data segment does not exist
-                                  in this frame.')
+                raise ValueError('The specified PSD data segment does not exist' 
+                                 ' in this frame.')
             if (not data_set) & data_in_cache:
                 ifo.set_strain_data_from_frame_file(
                     frame_file=cache.path,