title: I am having trouble pushing my rails app to Heroku/getting the 'pg' gem to install?
body: <p>Originally I couldn't push my rails 4 app to heroku because my database was sqlite, and so now I have been trying to install the Postgresql gem ('pg') but I am not having any luck.  This is the error message I get in my terminal after running bundle install: </p>
  
  <pre><code>checking for pg_config... no
  No pg_config... trying anyway. If building fails, please try again with
  --with-pg-config=/path/to/pg_config
  checking for libpq-fe.h... no
  Can't find the 'libpq-fe.h header
  *** extconf.rb failed ***
  </code></pre>
  
  <p>After running<br>
      gem install pg -v '0.17.1' -–with-pg-config</p>
  
  <p>I get this error in my terminal:</p>
  
  <pre><code>ERROR:  While executing gem ... (Gem::Requirement::BadRequirementError)
   Illformed requirement ["0.17.1--with-pg_config"]
  /project$ gem install pg -v '0.17.1'--with-pg-config
  ERROR:  Could not find a valid gem 'pg' (= 0.17.1.pre..pre.with.pre.pg.pre.config) in   
  
  any repository
  ERROR:  Possible alternatives: pg
  </code></pre>
  
  <p>Thanks for the help.</p>